feat: implement pngx-controller with Gitea CI/CD deployment

- Full FastAPI sync engine: master→replica document sync via paperless REST API
- Web UI: dashboard, replicas, logs, settings (Jinja2 + HTMX + Pico CSS)
- APScheduler background sync, SSE live log stream, Prometheus metrics
- Fernet encryption for API tokens at rest
- pngx.env credential file: written on save, pre-fills forms on load
- Dockerfile with layer-cached uv build, Python healthcheck
- docker-compose with host networking for Tailscale access
- Gitea Actions workflow: version bump, secret injection, docker compose deploy

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

.env.example

@@ -0,0 +1,10 @@
+# Required: Fernet key for encrypting API tokens at rest
+# Generate with: python -c "from cryptography.fernet import Fernet; print(Fernet.generate_key().decode())"
+SECRET_KEY=
+
+# SQLite database path
+DATABASE_URL=sqlite:////data/db.sqlite3
+
+# Optional: seed settings on first boot
+MASTER_URL=http://100.x.x.x:8000
+MASTER_TOKEN=your-paperless-api-token