feat(backup): add database backup/restore with scheduled retention and admin dashboard

- Add BackupRecord model for tracking backup archives
- Add migration 021_add_backup_records
- Add backup configuration settings (backup_enabled, backup_dir, backup_remote_destination, backup_remote_folder, backup_retain_hourly/daily/weekly)
- Add backup_tasks.py with create_backup, cleanup_old_backups, and helpers
- Register hourly/daily/weekly Celery beat schedules
- Add /api/admin/backup/* REST endpoints (list, create, download, restore, delete, cleanup)
- Add /admin/backup dashboard view and template
- Add backup link to admin dropdown navigation in base.html
- Add backup settings to SETTING_METADATA in settings_service.py
- Add comprehensive test suite (39 tests passing)

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

migrations/versions/021_add_backup_records.py

@@ -0,0 +1,43 @@
+"""Add backup_records table for database backup tracking
+
+Revision ID: 021_add_backup_records
+Revises: 020_add_subscription_change_pending
+Create Date: 2026-03-07
+"""
+
+from typing import Union
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "021_add_backup_records"
+down_revision: Union[str, None] = "020_add_subscription_change_pending"
+depends_on: Union[str, None] = None
+
+
+def upgrade() -> None:
+    """Create backup_records table."""
+    op.create_table(
+        "backup_records",
+        sa.Column("id", sa.Integer(), nullable=False),
+        sa.Column("filename", sa.String(255), nullable=False),
+        sa.Column("local_path", sa.String(1024), nullable=True),
+        sa.Column("backup_type", sa.String(20), nullable=False),
+        sa.Column("size_bytes", sa.Integer(), nullable=False, server_default="0"),
+        sa.Column("checksum", sa.String(64), nullable=True),
+        sa.Column("status", sa.String(20), nullable=False, server_default="ok"),
+        sa.Column("remote_destination", sa.String(50), nullable=True),
+        sa.Column("remote_path", sa.String(1024), nullable=True),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now()),
+        sa.PrimaryKeyConstraint("id"),
+        sa.UniqueConstraint("filename"),
+    )
+    op.create_index("ix_backup_records_backup_type", "backup_records", ["backup_type"])
+    op.create_index("ix_backup_records_created_at", "backup_records", ["created_at"])
+
+
+def downgrade() -> None:
+    """Drop backup_records table."""
+    op.drop_index("ix_backup_records_created_at", "backup_records")
+    op.drop_index("ix_backup_records_backup_type", "backup_records")
+    op.drop_table("backup_records")