fix: repair broken examples and graduate UV runtime

[bryan-anthropic]

Summary

• hello-world-node (examples/hello-world-node installs but does not function on Claude desktop #200): Server crashes on initialize in Claude Desktop because server.connect(transport) was not awaited. Wrapped in async main() with proper error handling.
• hello-world-uv: mcpb pack fails because v0.4 schema requires mcp_config but the example omitted it. Added the required mcp_config block with uv run pattern.
• file-manager-python (Error of building DXT for examples/file-manager-python #47, Python File manager MCP example server doesn't run #72): Multiple failures — v0.1 manifest with privacy_policies (schema violation), command: "python" (ENOENT on macOS), no bundled deps. Converted to v0.4/uv runtime with proper mcp_config, cleaned up pyproject.toml, added .mcpbignore.
• UV graduation: Removed "experimental" labels from UV runtime across docs (MANIFEST.md, README.md) and schema comments.
• Default version bump: DEFAULT_MANIFEST_VERSION from "0.2" to "0.3" (v0.3 has been stable since Feb 2026).

Verification

All three examples smoke-tested locally:

Example	mcpb pack	MCP initialize (stdio)	tools/list
hello-world-node	496.6kB, 4 files	responds correctly	n/a (tested separately)
hello-world-uv	2.5kB, 5 files	responds correctly	1 tool (say_hello)
file-manager-python	2.2kB, 3 files	responds correctly	3 tools

• 109/109 tests pass
• No schema drift (JSON schemas regenerated cleanly)

Closes #200, closes #47, closes #72.

🤖 Generated with Claude Code

[bryan-anthropic]

Review by Claude Code

Multi-concern PR, but all changes fall under "fix broken examples and modernize." Observations:

hello-world-node (#200): Wrapping server.connect(transport) in an async main() with proper await fixes the race condition that caused crashes in Claude Desktop's UtilityProcess environment. Straightforward fix.

hello-world-uv: Adding the required mcp_config block aligns with the v0.4 schema mandate. Necessary for these examples to actually validate.

file-manager-python (#47, #72): The rewrite from broken v0.1/python to v0.4/uv is aggressive but correct. The old manifest had schema violations (privacy_policies: [], PYTHONPATH env, setuptools boilerplate) that would fail validation. The new command: "uv" with args: ["run", "--directory", "${__dirname}", "server/main.py"] follows the established uv pattern. The .mcpbignore addition is a nice touch.

UV graduation: Removing "experimental" labels from MANIFEST.md, README.md, schema comments, and the hello-world-uv README reflects the runtime's stability since early 2026. Consistent cleanup across all touchpoints.

DEFAULT_MANIFEST_VERSION 0.2 → 0.3: Worth noting this is a behavioral change — mcpb init will now scaffold v0.3 manifests. Reasonable given v0.3 has been stable since Feb 2026, but flagging for visibility since it affects new bundle authors.

Potential merge conflict: The .gitignore additions (CLAUDE.md, PROJECT_STATUS.md) overlap with PR #207. Whichever merges second will need a trivial conflict resolution.

No blocking issues. All examples were smoke-tested per the PR description (pack + initialize + tools/list).