fix(tests): raise jest timeouts to the 120s convention (stable) (#902)

Stable backport combining #860 (never reached stable) and #900:

- jest.config.js gains testTimeout: 120000 — stable still ran on Jest's
  5s default for anything unpinned, while its migration chain (134 core
  migrations via backports) is nearly as long as beta's.
- All 19 suite-level jest.setTimeout(30000/60000) pins raised to 120s;
  local pins override the config default (#860's rationale).
- All 15 hook-ARGUMENT timeout pins on migration-booting beforeAll
  hooks raised to 120s (#900's rationale — the 3.97.0-beta.0 release PR
  failed on exactly this class on the beta side).

Untouched: the three suites whose pinned hooks don't run migrations
(webhookDelivery, imageProcessor.storage, storageBackend) and
publicQuotes' 30s pin on the rate-limit lockout test.

No test logic changed.

Co-authored-by: Paul Nothaft <[email protected]>

backend/__tests__/integration/adminBackupIntegrity.test.js

@@ -29,7 +29,7 @@ jest.mock('../../src/middleware/permissions', () => ({
   requirePermission: () => (_req, _res, next) => next(),
 }));
 
-jest.setTimeout(30000);
+jest.setTimeout(120000);
 
 describe('GET /api/admin/system-health/backup-integrity', () => {
   let cleanup;