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

.env.example

@@ -1,30 +1,16 @@
 # Matrix homeserver
 MATRIX_HOMESERVER_URL=https://matrix.example.com
 
-# Matrix audit bot (pre-authenticated)
-MATRIX_AUDIT_ROOM_ID=!roomid:example.com
-MATRIX_BOT_USER_ID=@bot:example.com
+# Matrix bot (pre-authenticated)
+MATRIX_BOT_USER_ID=@melora-bot:example.com
 MATRIX_BOT_ACCESS_TOKEN=syt_bot_token_here
 
-# Radarr
-RADARR_URL=https://radarr.example.com
-RADARR_API_KEY=your_radarr_api_key
-RADARR_QUALITY_PROFILE_ID=1
-RADARR_ROOT_FOLDER=/movies
+# Matrix room for arrival announcements (unencrypted)
+MATRIX_ARRIVALS_ROOM_ID=!roomid:example.com
 
-# Sonarr
-SONARR_URL=https://sonarr.example.com
-SONARR_API_KEY=your_sonarr_api_key
-SONARR_QUALITY_PROFILE_ID=1
-SONARR_ROOT_FOLDER=/tv
+# Shared secret for *arr webhook authentication
+# Set the same value in each *arr instance under Settings → Connect → Webhook
+WEBHOOK_SECRET=your_shared_secret_here
 
-# Lidarr
-LIDARR_URL=https://lidarr.example.com
-LIDARR_API_KEY=your_lidarr_api_key
-LIDARR_QUALITY_PROFILE_ID=1
-LIDARR_ROOT_FOLDER=/music
-
-# App
-# SESSION_SECRET_KEY is auto-generated if omitted. A new key on every restart invalidates all sessions.
-# SESSION_SECRET_KEY=
-DATABASE_PATH=bellhop.db
+# SQLite database path
+DATABASE_PATH=melora.db