Three-phase MCP server startup: wait for Python READY handshake, send
_warmup command (pcbnew.BOARD() triggers wxApp init on macOS), connect
to MCP transport only after warm-up completes.
Also pre-populate symbol library cache during SymbolLibraryManager
init so the first search_symbols call doesn't parse 241 .kicad_sym
files from disk (30-120s). Both warm-up and cache population happen
before tools are registered with the MCP client.
Fixes#195