Add multi-speaker tracking with beam steering (#5)

multi_speaker.py: Tracks up to 2 speakers simultaneously. When 2 distinct
DoA angles are detected (30°+ apart) for >1s, locks the XVF3800's fixed
beams onto each speaker. Releases back to auto mode when only 1 speaker
remains (3s timeout). Manages beam gating so only the speaking beam is active.

xvf3800.py: Added beam steering commands — enable_fixed_beams(),
set_beam_azimuths(), enable_beam_gating(), read_all_beams().
Manager gets steer_beams() and release_beams() convenience methods.

headmic.py: Wire multi-speaker tracker into DoA loop. New endpoint:
GET /speakers/tracked — current speaker positions, beam mode, lock state.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

headmic.py

@@ -161,6 +161,7 @@ class ServiceState:
         self.doa: dict = {}               # latest DoA from both arrays
         self.spatial: Optional[dict] = None  # triangulated position + gaze
         self.last_anomaly: Optional[dict] = None  # last spatial anomaly detected
+        self.multi_speaker: Optional[dict] = None  # multi-speaker tracking state
 
 state = ServiceState()
 
@@ -177,6 +178,9 @@ binaural_recorder = None
 
 # Spatial scene
 spatial_scene = None
+
+# Multi-speaker tracker
+multi_speaker = None
 enrollment_name = None
 
 # Audio stream
@@ -439,6 +443,10 @@ def doa_track_loop():
         try:
             state.doa = xvf_manager.read_both_doa()
 
+            # Multi-speaker tracking (beam steering)
+            if multi_speaker:
+                state.multi_speaker = multi_speaker.update(state.doa)
+
             if spatial_tracker and dual_stream:
                 left_energy = dual_stream.left.get_energy() if dual_stream.left else 0.0
                 right_energy = dual_stream.right.get_energy() if dual_stream.right else 0.0
@@ -496,7 +504,7 @@ app = FastAPI(title="HeadMic", description="Vixy's Ears 🦊👂 (Dual XVF3800)"
 
 @app.on_event("startup")
 async def startup():
-    global sound_classifier, sound_ring_buffer, speaker_recognizer, dual_stream, LEDS_AVAILABLE, spatial_tracker, binaural_recorder, spatial_scene
+    global sound_classifier, sound_ring_buffer, speaker_recognizer, dual_stream, LEDS_AVAILABLE, spatial_tracker, binaural_recorder, spatial_scene, multi_speaker
 
     state.running = True
 
@@ -577,6 +585,12 @@ async def startup():
     spatial_scene = SpatialScene()
     spatial_scene.start()
 
+    # --- Multi-speaker tracking ---
+    if xvf_manager.left or xvf_manager.right:
+        from multi_speaker import MultiSpeakerTracker
+        multi_speaker = MultiSpeakerTracker(xvf_manager)
+        logger.info("Multi-speaker tracking enabled (2 beams per array)")
+
     # --- Binaural recording ---
     if os.environ.get("BINAURAL_RECORD", "").lower() in ("1", "true", "yes"):
         from binaural_recorder import BinauralRecorder
@@ -596,6 +610,8 @@ async def startup():
 async def shutdown():
     state.running = False
     leds_off()
+    if multi_speaker and xvf_manager:
+        xvf_manager.release_beams()
     if spatial_scene:
         spatial_scene.stop()
     if binaural_recorder:
@@ -666,6 +682,16 @@ async def doa():
     }
 
 
+# --- Multi-speaker ---
+
+@app.get("/speakers/tracked")
+async def tracked_speakers():
+    """Currently tracked speaker positions and beam state."""
+    if not state.multi_speaker:
+        return {"speakers": [], "beam_mode": "auto", "active_count": 0, "total_tracked": 0}
+    return state.multi_speaker
+
+
 # --- Spatial scene ---
 
 @app.get("/scene")