Make container more robust (#95)

Reviewed-on: #95

12 files changed (+149, -66)
Key changes:
1. Monolithic container — Replaced the two-service compose setup (backend + frontend/caddy) with a single timetracker container. Caddy is now built into the image rather than running as a separate container.
2. Supervisord process manager — Added supervisor.conf and installed supervisor in the Dockerfile. entrypoint.sh now delegates to supervisord to manage three processes: Caddy, Gunicorn, and Qcluster — replacing manual trap/signaling logic.
3. Bundled Caddy — The Dockerfile now downloads and installs Caddy v2.9.1 directly into the image (/usr/local/bin/caddy). The Caddyfile was updated to use reverse_proxy localhost:8001 and serves static files from /home/timetracker/app/static.
4. Configurable deployment — Added .env.example with configurable environment variables: TZ, PUID/PGID, TIMETRACKER_EXTERNAL_PORT, DATA_DIR, CSRF_TRUSTED_ORIGINS. docker-compose.yml now references these with sensible defaults.
5. UID/GID flexibility — entrypoint.sh uses usermod/groupmod at startup to remap the timetracker user to the host-specified PUID/PGID, avoiding permission issues with mounted volumes.
6. Database & static files — settings.py now respects DATA_DIR env var for the SQLite database path. STATIC_ROOT changed to BASE_DIR / "static".
7. Dev improvements — New Caddyfile.dev (with browse enabled for static files) and updated Makefile dev-prod target runs Caddy alongside Django in development.
8. Tests — Re-enabled the test step in the Docker build GitHub Actions workflow.

Caddyfile

@@ -1,14 +1,15 @@
-{ 
-    auto_https off
-    admin off
+{
+	auto_https off
 }
 
 :8000 {
-    handle_path /static/* {
-        root * /usr/share/caddy
-        file_server
-    }
-    handle {
-        reverse_proxy backend:8001
-    }
-}
+	handle_path /static/* {
+		root * /home/timetracker/app/static
+		file_server
+	}
+	handle /robots.txt {
+		root * /home/timetracker/app/games/static
+		file_server
+	}
+	reverse_proxy localhost:8001
+}