fix: add cross-platform commit helper to resolve heredoc issues

[PierrunoYT]

Summary

Fixes #274 - Git commit fails on Windows PowerShell due to heredoc syntax issues and improper shell detection.

This PR provides a comprehensive two-part solution to resolve cross-platform terminal execution issues:

Root Cause Analysis

The issue had two components:

1. Shell Detection: Terminal commands on Windows always defaulted to cmd.exe, ignoring the actual shell (PowerShell)
2. Heredoc Syntax: Bash heredoc syntax (<<'EOF') doesn't work in any Windows shell (cmd.exe or PowerShell)

Part 1: Cross-Platform Commit Helper

• Add scripts/commit-helper.ts: Cross-platform commit script using temporary files instead of heredocs
• Add npm script: "commit": "bun scripts/commit-helper.ts" for easy access via npm run commit "message"
• Update system prompt: Modified backend/src/system-prompt/prompts.ts to instruct AI agents to use the commit helper
• Replace platform-specific instructions: Single helper approach instead of separate Unix/Windows instructions

Part 2: PowerShell Detection Fix

• Fix npm-app/src/terminal/background.ts: Add proper shell detection using detectShell()
• Fix sdk/src/tools/run-terminal-command.ts: Apply same detection logic to SDK
• Correct shell arguments: Use -Command for PowerShell and /c for cmd.exe
• Import detection utility: Utilize existing detectShell() function

How it works

Commit Helper:

• Validates git repository state and staged changes
• Writes commit messages to temporary files (cross-platform compatible)
• Uses git commit -F tempfile to read the message
• Handles multi-line messages correctly on Windows, macOS, and Linux
• Provides proper error handling and cleanup

Shell Detection:

• Detects whether user is running PowerShell or cmd.exe on Windows
• Routes commands to the appropriate shell with correct arguments
• Maintains compatibility with existing Unix shell handling

Usage

npm run commit "Your multi-line commit message here

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Benefits

• Eliminates heredoc failures: AI agents no longer use problematic heredoc syntax
• Proper shell routing: Commands execute in the correct shell environment
• Cross-platform consistency: Works reliably across all operating systems
• Maintains functionality: Existing commands continue to work as expected
• Future-proof: Handles both current and future shell detection scenarios

This comprehensive solution ensures AI agents can create proper multi-line commits regardless of the operating system or shell environment.

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