Add backup/restore tooling and guidance

[JSONbored]

Problem: Zero backup/restore tooling or guidance exists anywhere for AMS state, unlike the main product's dedicated backup scripts and freshness monitoring.

Area: AMS / Self-host

Proposal: Add a simple backup/restore script (even a straightforward file-copy-based one, given these are local SQLite files) and document the procedure.

Deliverables:

• A working backup/restore script and accompanying documentation.

[linear-code]

JSO-3532