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.

.gitignore

@@ -1,3 +1,9 @@
-__pycache__
-*egg-info
+__pycache__/
+*.py[cod]
+.venv/
+var/
+.pytest_cache/
+.mypy_cache/
+*.egg-info/
 build/
+dist/