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.

.dockerignore

@@ -0,0 +1,11 @@
+.git
+.venv
+__pycache__/
+*.pyc
+*.pyo
+.pytest_cache/
+.mypy_cache/
+var/
+dist/
+build/
+*.egg-info/