Implement Melora: *arr media arrival webhook announcer for Matrix

Replace Bellhop scaffolding with full Melora implementation:
- FastAPI webhook endpoints for Radarr, Sonarr, and Lidarr
- matrix-nio integration with threaded room posting
- SQLite for thread root persistence and event deduplication
- Message formatting with plain text and HTML for each media type
- Shared secret authentication via X-Arr-Webhook-Secret header
- Updated dependencies, configuration, and documentation

https://claude.ai/code/session_01DuzWyMMXvLMB4VxEwJyV4X

app/main.py

@@ -0,0 +1,46 @@
+import logging
+from contextlib import asynccontextmanager
+
+from fastapi import FastAPI
+
+from app.database import close_db, get_thread_root, init_db, set_thread_root
+from app.matrix import THREAD_ROOT_MESSAGES, close_client, send_thread_root
+from app.webhooks import router as webhook_router
+
+logging.basicConfig(
+    level=logging.INFO,
+    format="%(asctime)s %(levelname)s %(name)s: %(message)s",
+)
+log = logging.getLogger(__name__)
+
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    log.info("Starting Melora")
+    await init_db()
+    await _ensure_thread_roots()
+    log.info("Melora ready")
+    yield
+    log.info("Shutting down Melora")
+    await close_client()
+    await close_db()
+
+
+async def _ensure_thread_roots() -> None:
+    for media_type in THREAD_ROOT_MESSAGES:
+        existing = await get_thread_root(media_type)
+        if existing:
+            log.info("Thread root for %s: %s", media_type, existing)
+            continue
+        log.info("Creating thread root for %s", media_type)
+        event_id = await send_thread_root(media_type)
+        await set_thread_root(media_type, event_id)
+
+
+app = FastAPI(title="Melora", lifespan=lifespan)
+app.include_router(webhook_router)
+
+
+@app.get("/health")
+async def health():
+    return {"status": "ok"}