Adds voice-based speaker ID triggered by YAMNet speech detection.
New speaker_id.py module with SQLite-backed voice enrollment and
cosine similarity matching. Endpoints: POST /speakers/enroll,
POST /speakers/enroll-from-mic, GET /speakers, DELETE /speakers/{name}.
Orange LED animation during enrollment.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
