feat: initial logwatch – Watchtower ntfy noise filter

Subscribes to an ntfy channel via JSON stream, filters Watchtower
notifications by importance (updates, failures, errors) and forwards
only the relevant ones to a second ntfy channel.

- filter.py: SSE consumer + regex-based importance filter + forwarder
- Dockerfile + docker-compose.yml for containerised deployment
- Configurable via env vars (SOURCE_URL, TARGET_URL, LOG_LEVEL, …)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -0,0 +1,15 @@
+services:
+  logwatch:
+    build: .
+    image: logwatch:latest
+    container_name: logwatch
+    restart: unless-stopped
+    environment:
+      # ntfy source channel (your Watchtower notifications)
+      - SOURCE_URL=http://192.168.123.77/albert
+      # ntfy target channel (where important stuff goes)
+      - TARGET_URL=http://192.168.123.77/wichtig
+      # optional: Bearer token if target channel needs auth
+      # - TARGET_TOKEN=your-token-here
+      - LOG_LEVEL=INFO
+      - RECONNECT_DELAY=10