Fixes the bare-python3 fragility that broke voice-bridge for users who had
'brew install <X-with-python-dep>' shift PATH resolution to a Python
without voice_bridge installed. Plugin and npm shim now invoke the
voice-bridge-mcp console script directly; install ladders prefer
'uv tool install' for isolation.

See PYTHON_AUDIT_HANDOFF.md and RELEASE_0.1.5_HANDOFF.md (private,
not in repo) for full root-cause + release context.