Adds comprehensive local KiCad symbol library search functionality and fixes KICAD9_3RD_PARTY environment variable resolution.
Features:
- Symbol library search by name, LCSC ID, description, manufacturer, MPN
- Support for 3rd party libraries installed via Plugin and Content Manager
- New MCP tools: search_symbols, list_symbol_libraries, get_symbol_info
- Enhanced library path resolution for KiCad 8 and 9
This enables users with locally installed JLCPCB libraries to search and use components directly.
Co-authored-by: l3wi <l3wi@users.noreply.github.com>