fix(04-02): use fileParallelism:false to prevent DB test race conditions

Replaced singleFork:true + sequence config with the simpler fileParallelism:false
which correctly serializes test file execution. The previous singleFork approach
ran tests from multiple files concurrently within one process, allowing the global
afterEach cleanup (test/setup.ts: truncates lists/listShares) to delete rows mid-test
in another file, causing intermittent FK violations (ER_DUP_ENTRY, ER_NO_REFERENCED_ROW).

fileParallelism:false runs one test file at a time so afterEach cleanup for file A
never races with insertions from file B.

apps/api/vitest.config.ts

@@ -5,17 +5,10 @@ export default defineConfig({
     environment: 'node',
     globals: true,
     setupFiles: ['./test/setup.ts'],
-    // Run test files sequentially so concurrent DB tests do not interfere via
-    // the shared MariaDB (global afterEach in test/setup.ts truncates list tables
-    // which causes FK violations if two workers share the DB concurrently).
-    sequence: {
-      concurrent: false,
-    },
-    pool: 'forks',
-    // singleFork: top-level in vitest 4.x (poolOptions removed in v4).
-    // Runs all test files in one forked process so the shared MariaDB
-    // teardown (afterEach in test/setup.ts) never races with inserts
-    // from a concurrent worker.
-    singleFork: true,
+    // Disable parallel file execution so concurrent DB tests do not interfere
+    // via the shared MariaDB. The global afterEach in test/setup.ts truncates
+    // list tables; running test files in parallel causes FK violations when one
+    // file's afterEach deletes rows that another file's test is still using.
+    fileParallelism: false,
   },
 })