feat: spirit engine — seance WS, entity minting/Codex, Piper TTS voices, wire telemetry

- WS /ws/session: modes, summon, anomaly fragments, streaming direct contact,
  passive wire-ghost ambient loop, per-user rate limits, event transcript
- entities: anomaly-signature fingerprinting, LLM minting + procedural
  fallback, Codex matching with contact counts and sightings
- tts: 8 local Piper voices (EN/ES), per-entity voice profiles, numpy
  effects chain (pitch/rate/bitcrush/echo/static)
- llm: streaming client, submit_stream in bounded queue, SpiritService
  with offline fallbacks for every channel
- routes: public /api/codex, /api/codex/{id}, /api/stats; /audio static mount
- models: Entity, EntitySighting, Event, ContactSession(entity_id, language)

backend/app/models/entity_sighting.py

@@ -0,0 +1,23 @@
+import uuid
+from datetime import datetime, timezone
+
+from sqlalchemy import DateTime, ForeignKey
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.db import Base
+
+
+class EntitySighting(Base):
+    """Join row: this session contacted this Codex entity."""
+
+    __tablename__ = "entity_sightings"
+
+    id: Mapped[uuid.UUID] = mapped_column(primary_key=True, default=uuid.uuid4)
+    entity_id: Mapped[uuid.UUID] = mapped_column(ForeignKey("entities.id"), index=True)
+    session_id: Mapped[uuid.UUID] = mapped_column(
+        ForeignKey("contact_sessions.id"), index=True
+    )
+    user_id: Mapped[uuid.UUID] = mapped_column(ForeignKey("users.id"))
+    seen_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), default=lambda: datetime.now(timezone.utc)
+    )