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>

pyproject.toml

@@ -5,12 +5,18 @@ description = "Persistent, autonomous AI assistant"
 readme = "README.md"
 requires-python = ">=3.11"
 dependencies = [
+    "fastapi>=0.115",
     "httpx>=0.28.1",
     "numpy>=2.4.5",
     "openai>=2.37.0",
     "python-dotenv>=1.2.2",
+    "uvicorn[standard]>=0.34",
 ]
 
+[project.scripts]
+lyra = "lyra.__main__:main"
+lyra-web = "lyra.web.server:serve"
+
 [dependency-groups]
 dev = [
     "pytest>=8.0",