feat(examples): add hello-world and code-stats example plugins

Add two example plugins demonstrating plugin capabilities:

1. hello-world (basic):
   - Command: /hello [name] - greets the user
   - Hook: tool_execute_before - logs tool executions
   - Config: greeting_prefix setting

2. code-stats (advanced):
   - Commands: /stats, /stats-reset, /stats-export
   - Hooks: file_operation_after, session_end, widget_register
   - UI widget: Status bar showing code statistics
   - Event system: Custom events for integrations

Both plugins include complete manifest, Cargo.toml, and documentation.

Author: echobt

examples/plugins/code-stats/Cargo.toml

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+[package]
+name = "code-stats-plugin"
+version = "1.0.0"
+edition = "2021"
+description = "Tracks and displays code statistics including lines added, removed, and files modified"
+authors = ["Cortex Team <team@cortex.dev>"]
+license = "MIT"
+
+# Build for WASM target: cargo build --target wasm32-wasi --release
+
+[lib]
+crate-type = ["cdylib"]
+
+[dependencies]
+wee_alloc = "0.4"
+
+[profile.release]
+opt-level = "s"
+lto = true

examples/plugins/code-stats/README.md

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+# Code Stats Plugin
+
+An advanced example plugin demonstrating comprehensive Cortex plugin capabilities.
+
+## Features
+
+### Commands
+
+- **`/stats`** (aliases: `/statistics`, `/metrics`) - Display current session code statistics
+- **`/stats-reset`** (alias: `/reset-stats`) - Reset all statistics counters to zero
+- **`/stats-export`** (alias: `/export-stats`) - Export statistics to JSON format
+
+### Hooks
+
+- **`file_operation_after`** - Tracks statistics after each file operation
+- **`session_end`** - Saves statistics when the session ends
+- **`widget_register`** - Registers the status bar widget
+
+### UI Widget
+
+- **Status Bar Widget** - Displays compact statistics (`+123 -45 (67)`) in the status bar
+
+### Configuration
+
+- **`auto_save`** (boolean, default: true) - Automatically save stats on session end
+- **`display_format`** (string, default: "compact") - Format for displaying stats (compact, detailed)
+- **`track_by_language`** (boolean, default: true) - Track statistics per programming language
+
+## Project Structure
+
+```
+code-stats/
+├── plugin.toml     # Plugin manifest (metadata, commands, hooks, config)
+├── Cargo.toml      # Rust build configuration
+├── src/
+│   └── lib.rs      # Plugin implementation
+└── README.md       # This file
+```
+
+## Building
+
+### Prerequisites
+
+1. Install Rust: https://rustup.rs/
+2. Add the WASM target:
+   ```bash
+   rustup target add wasm32-wasi
+   ```
+
+### Build the Plugin
+
+```bash
+cd examples/plugins/code-stats
+cargo build --target wasm32-wasi --release
+```
+
+The compiled WASM module will be at:
+```
+target/wasm32-wasi/release/code_stats_plugin.wasm
+```
+
+## Installing
+
+Copy the compiled WASM and manifest to your Cortex plugins directory:
+
+```bash
+# Create plugin directory
+mkdir -p ~/.cortex/plugins/code-stats
+
+# Copy manifest
+cp plugin.toml ~/.cortex/plugins/code-stats/
+
+# Copy compiled WASM
+cp target/wasm32-wasi/release/code_stats_plugin.wasm ~/.cortex/plugins/code-stats/plugin.wasm
+```
+
+## Configuration
+
+Add to your Cortex configuration to customize the plugin:
+
+```toml
+[plugins.code-stats]
+enabled = true
+auto_save = true
+display_format = "detailed"  # or "compact"
+track_by_language = true
+```
+
+## Usage
+
+### View Statistics
+
+```
+/stats
+```
+
+Output: `Lines: +123 -45 | Files: 10 modified, 3 created, 1 deleted | Total ops: 14`
+
+### Reset Statistics
+
+```
+/stats-reset
+```
+
+This clears all counters to zero for a fresh start.
+
+### Export Statistics
+
+```
+/stats-export
+```
+
+Exports statistics as JSON to the event stream:
+
+```json
+{
+  "lines_added": 123,
+  "lines_removed": 45,
+  "files_modified": 10,
+  "files_created": 3,
+  "files_deleted": 1,
+  "total_operations": 14
+}
+```
+
+## Plugin Architecture
+
+### Statistics Tracking
+
+The plugin uses atomic counters to track:
+- **lines_added** - Total lines of code added
+- **lines_removed** - Total lines of code removed
+- **files_modified** - Number of files edited
+- **files_created** - Number of new files created
+- **files_deleted** - Number of files removed
+- **total_operations** - Total file operations
+
+### Event System
+
+The plugin emits events for external integrations:
+
+| Event Name | Trigger | Data |
+|------------|---------|------|
+| `code_stats.displayed` | `/stats` command | Current stats JSON |
+| `code_stats.before_reset` | `/stats-reset` command | Stats before reset |
+| `code_stats.exported` | `/stats-export` command | Full stats JSON |
+| `code_stats.session_end` | Session ending | Final stats JSON |
+| `code_stats.session_final` | Plugin shutdown | Final stats JSON |
+
+### Widget Rendering
+
+The status bar widget displays a compact summary:
+```
++{lines_added} -{lines_removed} ({total_ops})
+```
+
+Example: `+123 -45 (14)`
+
+## Development
+
+### Adding New Metrics
+
+1. Add an atomic counter in `src/lib.rs`:
+   ```rust
+   static MY_METRIC: AtomicU64 = AtomicU64::new(0);
+   ```
+
+2. Update the `get_stats_summary()` function to include it.
+
+3. Update the `get_stats_json()` function to include it.
+
+4. Add a recording function:
+   ```rust
+   fn record_my_metric(value: u64) {
+       MY_METRIC.fetch_add(value, Ordering::Relaxed);
+   }
+   ```
+
+### Adding New Commands
+
+1. Add the command definition in `plugin.toml`:
+   ```toml
+   [[commands]]
+   name = "my-command"
+   description = "My new command"
+   usage = "/my-command [args]"
+   ```
+
+2. Implement the handler in `src/lib.rs`:
+   ```rust
+   #[no_mangle]
+   pub extern "C" fn cmd_my_command() -> i32 {
+       log_info("My command executed!");
+       0
+   }
+   ```
+
+### Adding New Hooks
+
+1. Add the hook definition in `plugin.toml`:
+   ```toml
+   [[hooks]]
+   hook_type = "tool_execute_after"
+   priority = 100
+   function = "hook_tool_execute_after"
+   ```
+
+2. Implement the handler in `src/lib.rs`:
+   ```rust
+   #[no_mangle]
+   pub extern "C" fn hook_tool_execute_after() -> i32 {
+       log_debug("Tool execution completed");
+       0
+   }
+   ```
+
+## API Reference
+
+### Exported Functions
+
+| Function | Purpose | Returns |
+|----------|---------|---------|
+| `init()` | Plugin initialization | 0 on success |
+| `shutdown()` | Plugin cleanup | 0 on success |
+| `cmd_stats()` | Display stats | 0 on success |
+| `cmd_stats_reset()` | Reset counters | 0 on success |
+| `cmd_stats_export()` | Export JSON | 0 on success |
+| `hook_file_operation_after()` | Track file ops | 0 to continue |
+| `hook_session_end()` | Save on exit | 0 to continue |
+| `hook_widget_register()` | Register widget | 0 to continue |
+| `widget_render_code_stats()` | Render widget | 0 on success |
+| `api_get_stats_json()` | Get stats JSON | Length or error |
+
+### Host Functions Used
+
+| Function | Purpose |
+|----------|---------|
+| `log(level, ptr, len)` | Logging |
+| `get_context()` | Access host context |
+| `register_widget(region, ptr, len)` | Register UI widget |
+| `show_toast(level, ptr, len, duration)` | Show notification |
+| `emit_event(name_ptr, name_len, data_ptr, data_len)` | Emit custom event |
+
+## Testing
+
+The plugin can be tested by:
+
+1. Building and installing the plugin
+2. Performing various file operations in Cortex
+3. Running `/stats` to verify tracking
+4. Running `/stats-reset` and verifying counters reset
+5. Running `/stats-export` and verifying JSON output
+
+## License
+
+MIT License - See LICENSE file for details.

examples/plugins/code-stats/plugin.toml

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+# Code Stats Plugin - An advanced Cortex plugin example
+#
+# This plugin demonstrates advanced plugin capabilities:
+# - Multiple commands with different functionalities
+# - Multiple hooks for tracking file operations
+# - UI widget for status bar display
+# - Persistent storage across sessions
+
+# Top-level capabilities (before [plugin] section)
+capabilities = ["commands", "hooks", "config", "events"]
+
+# Permissions for file operations
+permissions = [
+    { read_file = { paths = ["**/*"] } },
+]
+
+[plugin]
+id = "code-stats"
+name = "Code Statistics Plugin"
+version = "1.0.0"
+description = "Tracks and displays code statistics including lines added, removed, and files modified"
+authors = ["Cortex Team <team@cortex.dev>"]
+homepage = "https://github.com/cortex/examples/plugins/code-stats"
+license = "MIT"
+min_cortex_version = "0.5.0"
+keywords = ["statistics", "metrics", "productivity", "advanced", "demo"]
+
+# Command definitions
+[[commands]]
+name = "stats"
+aliases = ["statistics", "metrics"]
+description = "Display current session code statistics"
+usage = "/stats"
+category = "analytics"
+
+[[commands]]
+name = "stats-reset"
+aliases = ["reset-stats"]
+description = "Reset all statistics counters to zero"
+usage = "/stats-reset"
+category = "analytics"
+
+[[commands]]
+name = "stats-export"
+aliases = ["export-stats"]
+description = "Export statistics to JSON format"
+usage = "/stats-export [filename]"
+category = "analytics"
+
+[[commands.args]]
+name = "filename"
+description = "Output filename for exported stats (defaults to 'stats.json')"
+required = false
+default = "stats.json"
+arg_type = "string"
+
+# Hook definitions
+[[hooks]]
+hook_type = "file_operation_after"
+priority = 50
+function = "hook_file_operation_after"
+
+[[hooks]]
+hook_type = "session_end"
+priority = 100
+function = "hook_session_end"
+
+[[hooks]]
+hook_type = "widget_register"
+priority = 50
+function = "hook_widget_register"
+
+# Configuration schema
+[config]
+auto_save = { description = "Automatically save stats on session end", type = "boolean", default = true, required = false }
+display_format = { description = "Format for displaying stats (compact, detailed)", type = "string", default = "compact", required = false }
+track_by_language = { description = "Track statistics per programming language", type = "boolean", default = true, required = false }
+
+[config.display_format.validation]
+enum_values = ["compact", "detailed"]
+
+# WASM module settings
+[wasm]
+memory_pages = 256
+timeout_ms = 10000
+wasi_enabled = true
+wasi_caps = ["stdout", "stderr", "clocks"]