Improve add_component reliability & MCP context (#109)

[renardeinside]

Summary

• Structured add_component response: Replace plain-text success message with JSON including written_files, unchanged_files, dependencies_installed, auto_detected_deps, css_updated, and warnings
• Auto-detect missing npm deps: Scan component file imports for 3rd-party packages not in package.json or registry spec deps, auto-install them via bun add
• Improved docs search ranking: Add bm25() column weighting (entity=5.0, symbols=3.0) and PascalCase entity boosting with hint word stripping ("fields", "attributes")
• CLAUDE.md template: Add registry-aware guidance and missing list_registry_components + routes tools to MCP reference table

Test plan

• cargo build passes
• cargo test -p apx-core — all 162 tests pass (7 new)
• cargo clippy + cargo fmt clean
• Manual: run MCP server, call add_component for a component with 3rd-party imports, verify structured response with auto_detected_deps
• Manual: search "GenieAttachment fields" in docs tool, verify dataclass fields in top results
• Manual: apx init a new project, verify CLAUDE.md contains registry guidance

Closes #109

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