Group inventory: include campaign inventories in maintenance export/backup scripts

[prodmodfour]

Goal

Make sure group inventory data is not missed by maintenance export/backup flows.

Scope

• Update SQLite JSON export/backup scripts to include group_inventories.
• Add tests proving exported data includes group inventory documents with revision and updatedAt fields.
• If import/migration helpers have central table assumptions, update them to tolerate or restore group inventory data.
• Keep this limited to maintenance scripts and tests.

Acceptance criteria

• Existing export tests still pass.
• New export test includes at least one group inventory document.
• Running the export script does not silently drop group inventory state.
• No UI or API behavior changes are added in this ticket.

Depends on

• Group inventory: add SQLite migration for campaign inventories #28
• Group inventory: add SQLite repository with revision-checked updates #29