Move activity-log rotation out of scan coordination

[devjusty]

Parent

#8 — Spec: Session-only scan coordination (ADR-0001)

What to build

Admins can still rotate the activity log from Admin, but that behaviour no longer lives on the scan coordinator. The Session interface stops carrying log-rotation actions or pending flags. After this ticket, scan coordination is only about Scan Sessions and Capabilities — activity-log ops have their own home.

Acceptance criteria

• Activity-log rotation still works from Admin (same user-visible behaviour).
• The scan coordinator no longer exposes rotate / is-rotating on its Session interface.
• App → Admin wiring uses the new activity-log owner, not the scan coordinator.
• Existing tests updated; scan-coordinator tests no longer assert rotation surface.

Blocked by

None — can start immediately.

[devjusty]

Implemented on main: activity-log rotation lives in useActivityLog; App wires Admin from that hook; useScan / ScanContext no longer expose rotate / is-rotating.