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.py

@@ -0,0 +1,34 @@
+import uuid
+from datetime import datetime, timezone
+
+from sqlalchemy import DateTime, ForeignKey, Integer, String, Text
+from sqlalchemy.dialects.postgresql import JSONB
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.db import Base
+
+RARITY_TIERS = ("common", "uncommon", "rare", "mythic")
+
+
+class Entity(Base):
+    """A spirit in the Codex: minted from a session's anomaly signature,
+    or matched again on a later contact."""
+
+    __tablename__ = "entities"
+
+    id: Mapped[uuid.UUID] = mapped_column(primary_key=True, default=uuid.uuid4)
+    name: Mapped[str] = mapped_column(String(64), unique=True, index=True)
+    epithet: Mapped[str] = mapped_column(String(128), default="")
+    persona: Mapped[str] = mapped_column(Text, default="")
+    rarity_tier: Mapped[str] = mapped_column(String(16), default="common", index=True)
+    signature: Mapped[str] = mapped_column(String(64), unique=True, index=True)
+    voice_profile: Mapped[dict] = mapped_column(JSONB, default=dict)
+    visual_profile: Mapped[dict] = mapped_column(JSONB, default=dict)
+    sample_quotes: Mapped[list] = mapped_column(JSONB, default=list)
+    contact_count: Mapped[int] = mapped_column(Integer, default=0)
+    discovered_by: Mapped[uuid.UUID | None] = mapped_column(
+        ForeignKey("users.id"), nullable=True
+    )
+    discovered_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), default=lambda: datetime.now(timezone.utc)
+    )