Remove three stale lint suppressions; say which DB the migrator manages

[Sbussiso]

Two accuracy fixes found during the second system review. Neither changes
behaviour.

1. Three lint suppressions that suppress nothing

eslint reports all three as unused directives — the rule no longer fires
on those lines, because the dependency arrays were completed and the
eslint-disable comments were left behind.

AdminPage.jsx was a plain duplicate:

    // eslint-disable-next-line react-hooks/exhaustive-deps
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [organization?.id, hasAdminFeature])

The first applied to the second comment rather than to any code.

Why this matters more than "3 warnings": a stale exhaustive-deps
suppression silently swallows the next genuine missing dependency on that
line. That's a real bug class in effect hooks — stale closures reading old
state — and it's precisely what the rule exists to catch. The explanatory
comments above two of them ("orgId: tear down + reconnect the stream under
the new org's token") are kept; only the dead directives go.

Lint: 47 → 44 problems, still 0 errors.

2. The migrator says SQLite; it manages production Postgres

app/core/migrations.py opened with "Lightweight schema sync for SQLite",
and every caveat in it is written in SQLite terms — which reads as though it
were self-host-only machinery.

It isn't. main.py calls sync_schema(engine, Base.metadata) unconditionally
on every boot against whatever engine is configured, and there is no Alembic
in this repo, so on Fly this module plus create_all() is the production
Postgres schema management. The header now says so, and notes where the SQLite
caveats read differently on Postgres (an ADD COLUMN with a non-volatile
default is metadata-only on PG11+, where SQLite rewrites).

Verified

• ruff check → All checks passed
• pytest → 864 passed
• npm run lint → exit 0, 44 warnings

🤖 Generated with Claude Code