fix(mcp): replay terminal localization evidence

[zzet]

Summary

• retain a deterministic, bounded localization evidence digest and final response at answer-ready
• replay the terminal answer idempotently for later navigation calls while keeping model-visible replay compact
• preserve the full terminal contract and digest in host metadata
• authenticate compact replay in the PostToolUse hook without weakening the existing visible-contract path
• cover concurrency, lifecycle, malformed boundaries, sanitization, replay size, host-loop behavior, and tamper rejection

Verification

• go test ./internal/mcp ./internal/hooks -count=1
• go test -race -p 1 ./internal/...
• golangci-lint run ./...
• git diff --check