feat: add Django backend foundation and Docker runtime

Add a Django admin-backed management layer for pobsync configs, runs,
snapshots, and schedules. Keep the existing CLI engine as the execution
source of truth, add import/run management commands, and provide SQLite
default plus optional MariaDB Docker Compose support.

src/pobsync_server/wsgi.py

@@ -0,0 +1,10 @@
+from __future__ import annotations
+
+import os
+
+from django.core.wsgi import get_wsgi_application
+
+
+os.environ.setdefault("DJANGO_SETTINGS_MODULE", "pobsync_server.settings")
+
+application = get_wsgi_application()