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/config.py

@@ -0,0 +1,18 @@
+import os
+from dotenv import load_dotenv
+
+load_dotenv()
+
+
+class Config:
+    MATRIX_HOMESERVER_URL: str = os.environ["MATRIX_HOMESERVER_URL"]
+    MATRIX_BOT_USER_ID: str = os.environ["MATRIX_BOT_USER_ID"]
+    MATRIX_BOT_ACCESS_TOKEN: str = os.environ["MATRIX_BOT_ACCESS_TOKEN"]
+    MATRIX_ARRIVALS_ROOM_ID: str = os.environ["MATRIX_ARRIVALS_ROOM_ID"]
+
+    WEBHOOK_SECRET: str = os.environ["WEBHOOK_SECRET"]
+
+    DATABASE_PATH: str = os.getenv("DATABASE_PATH", "melora.db")
+
+
+config = Config()