feat: persona chat loop, web UI, and local (Ollama) embeddings

Phase 1 — persona + persistent memory chat loop:
- lyra/persona.py + personas/lyra.md: editable identity/voice (friend-first,
  honest, never invents poker math)
- lyra/chat.py: turn loop assembling persona + cross-session recall + recent
  context, persisting both sides to SQLite
- lyra/session.py, lyra/__main__.py: session lifecycle + `lyra` REPL

Phase 1.25 — reuse the old web UI:
- vendored the prior single-page UI into lyra/web/static, repointed to
  same-origin
- lyra/web/server.py (FastAPI): serves the UI and backs its endpoint contract
  (/v1/chat/completions, session CRUD, health, inert thinking-stream) with the
  new chat loop + memory; SQLite stays the single source of truth
- `lyra-web` console script

Local backends — test for free, no OpenAI key:
- llm.embed routes via EMBED_BACKEND (cloud=OpenAI, local=Ollama /api/embed)
- simplified UI backend selector to Local (Ollama) / Cloud (OpenAI), default local
- memory connection opened check_same_thread=False for the threaded server

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lyra/session.py

@@ -0,0 +1,20 @@
+"""Session lifecycle. A session is one sitting (a poker session, or any chat).
+
+For now a session is just an id and a start time; later the poker domain pack
+will hang structured data (hands, stacks, villains) off the same id.
+"""
+from __future__ import annotations
+
+import secrets
+from dataclasses import dataclass, field
+from datetime import datetime, timezone
+
+
+def _new_id() -> str:
+    return "sess-" + secrets.token_hex(4)
+
+
+@dataclass
+class Session:
+    id: str = field(default_factory=_new_id)
+    started_at: str = field(default_factory=lambda: datetime.now(timezone.utc).isoformat())