test(integration): add DB integration tests for students, promotions, roles, modules

Covers full CRUD for each resource via testDb:
- promotions: list, create, get by id, not found, update, delete
- students: list, filter by promo, create, get, not found, update, delete
- roles: list, create, get with permissions, update+reset perms, delete
- modules: list, create, duplicate id rejection, get, not found, update, delete

27 integration tests passing in CI (act + Gitea Actions).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/integration/users_test.ts

@@ -1,6 +1,5 @@
 import { assertEquals, assertExists } from "@std/assert";
 import {
-  closeTestPool,
   seedRoles,
   seedUsers,
   testDb,
@@ -48,11 +47,3 @@ Deno.test({
   sanitizeOps: false,
 });
 
-Deno.test({
-  name: "integration: cleanup - close pool",
-  async fn() {
-    await closeTestPool();
-  },
-  sanitizeResources: false,
-  sanitizeOps: false,
-});