fix(server): an app on tables of its own starts its sample afresh

[MoSofi]

An app installed again on tables of its own starts its sample afresh.

The case. An app is removed and installed again, and the new install reuses none of the earlier tables: they were dropped with it, or they were an older version's under plain names. The earlier install's list of sample rows was still counted with the new one, which doubled the count shown.

The change.

• At install, a kept sample list is marked dropped when the install reuses no table. Where tables are reused, the list is taken back as before (already on main).
• When the sample is next added and a dropped list's table is still there, that table is emptied first. It is the app's own bookkeeping table (<app>_sample_data: which rows are sample), never one of its data tables. Rows an earlier version left behind stay as ordinary rows.

Tests. Folded into app-sample-reinstall.test.ts: the released Point of Sale app on every engine the run can reach: still the sample over kept tables; afresh on tables of its own; afresh after its tables were dropped.

History. Written on 2026-10-08 and never merged. Rebuilt as one commit on today's main: the commit main already had was left out, one conflict in install-service.ts resolved by keeping main's check that the list's table exists, the changeset cut to what is new.