feat(scanner): add yaml frontmatter support for markdown files

implement optional yaml frontmatter parsing with description and tags fields.
frontmatter enhances search with score boosting (+0.5 description, +0.3 exact
tag, +0.15 partial tag, capped at 1.0 total boost). frontmatter is stripped
from read_doc output and included in list_all_docs metadata. supports flexible
tag formats (array or comma-separated). handles malformed yaml, 2kb size limit,
and multi-word queries gracefully.

Version 0.1.0

initial release of local-docs MCP server

features:
- multi-source documentation scanning (commands, project-docs, project-root)
- always-on caching with file watching and auto-invalidation
- fuzzy search across all markdown files
- safe path resolution with security checks
- configurable exclusions and file size limits
- comprehensive test coverage with concurrency safety

performance:
- efficient directory walking with filepath.WalkDir
- cache-based file list with configurable TTL
- debounced file watcher to minimize rescans

reliability:
- proper error handling and logging
- context-aware operations with cancellation support
- resource cleanup and goroutine management
- security validation against path traversal