feat(mcp): trace relevance + closure-collection + god-file rendering + cold-start handshake (#580)

Trace endpoint relevance (overloaded names resolve to the real implementation instead of an empty protocol/delegate stub), Swift closure-collection synthesizer, multi-phase god-file explore rendering, and serve --mcp cold-start handshake sped ~811ms→~90ms (proxy answers initialize/tools-list locally). Full suite green (1090 pass).