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>

Dockerfile

@@ -0,0 +1,16 @@
+FROM python:3.12-slim
+
+WORKDIR /app
+
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+
+COPY filter.py .
+
+ENV SOURCE_URL=http://192.168.123.77/albert
+ENV TARGET_URL=
+ENV TARGET_TOKEN=
+ENV LOG_LEVEL=INFO
+ENV RECONNECT_DELAY=10
+
+CMD ["python", "-u", "filter.py"]