Three admin pages had divergent inline error-code → user-copy switch
tables (with wording drift, including a stale "Settings → Integrations"
that should have been Admin). Consolidate into web/src/lib/styles/error-copy.json,
expose via web/src/lib/api/error-copy.ts (ERROR_COPY + copyForCode),
and refactor the three pages to import the helper.
Fixes the three-way drift; the only user-visible behavior change is
the quarantine page now correctly says "Admin → Integrations".
Sets up the JSON for the M7 Flutter client (#356) to consume the same
table.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
