test(gateway): cross-user-isolation cleanup honors dbAvailable (#1275)

The no-database skip path failed the file: createDb connects lazily, so
on an unreachable database 'handle' is set while nothing was inserted;
afterAll checked only 'handle' and its cleanup deletes threw
ECONNREFUSED, failing the suite despite 28/28 tests being skipped.

Caught live by the publish pipeline's verify gate (pipeline 2486,
first gated publish after #1277): the gate's no-DATABASE_URL PGlite
path runs 'pnpm test' without ci-postgres, cross-user-isolation hit
its dead-cleanup path, verify correctly failed closed and blocked all
publish steps (build/publish-npm/build-gateway skipped).

Verified both paths: DATABASE_URL=dead-port -> 28 skipped, file
PASSES (was the failure); live 5433 -> 28 passed. Sibling suites
checked: connector-lease.postgres.integration skips at describe level
(describe.skipIf) so its afterAll never runs unguarded.

apps/gateway/src/__tests__/cross-user-isolation.test.ts

@@ -190,7 +190,13 @@ beforeEach((ctx) => {
 });
 
 afterAll(async () => {
-  if (!handle) return;
+  // Cleanup only when the fixture actually installed rows. `handle` is set
+  // before the first query (createDb connects lazily), so on an unreachable
+  // database `handle` is truthy while nothing was inserted — cleanup must
+  // honor `dbAvailable` or the skip path fails the file with ECONNREFUSED in
+  // afterAll (caught live by the publish pipeline's no-DATABASE_URL verify
+  // step, pipeline 2486).
+  if (!handle || !dbAvailable) return;
   const db = handle.db;
 
   // Delete in dependency order (FK constraints)