test(api): Infra (health/db/schema/seed/env/migrate) — fill gaps + lifecycle test

Drives all infra src files to 100% (env.ts, db/client.ts, db/ensure-dir.ts,
db/migrate.ts, db/seed.ts, routes/health.ts).

- env.test.ts: dev defaults when unset, overrides when set (PORT coerced),
  CORS_ORIGINS parsing (trim + drop empties) and empty-fallback.
- db.test.ts: runMigrations idempotency; ensureDbDir no-op for non-file URLs
  and bare filenames (branch coverage).
- seed.test.ts: production guard — no dev users seeded when NODE_ENV=production.
- c8-ignore the migrate.ts/seed.ts CLI direct-run blocks (unreachable under vitest).

No lifecycle test (infra domain, per plan). No bugs found — infra code correct;
only coverage gaps. All 112 API tests green; typecheck + oxlint clean.

apps/api/test/db.test.ts

@@ -1,6 +1,8 @@
 import { describe, it, expect } from 'vitest';
 import { db } from '../src/db/client';
 import { user } from '../src/db/schema';
+import { runMigrations } from '../src/db/migrate';
+import { ensureDbDir } from '../src/db/ensure-dir';
 
 describe('database', () => {
   it('can query the migrated user table (empty)', async () => {
@@ -8,3 +10,21 @@ describe('database', () => {
     expect(rows).toEqual([]);
   });
 });
+
+describe('runMigrations', () => {
+  it('is idempotent — running again on an already-migrated DB does not throw', async () => {
+    // setup.ts already migrated the test DB once; re-running must be a no-op.
+    await expect(runMigrations()).resolves.toBeUndefined();
+    await expect(runMigrations()).resolves.toBeUndefined();
+  });
+});
+
+describe('ensureDbDir', () => {
+  it('is a no-op for a non-file: URL', () => {
+    expect(() => ensureDbDir('libsql://remote.example')).not.toThrow();
+  });
+
+  it('does not create a directory for a bare filename in the current dir', () => {
+    expect(() => ensureDbDir('file:app.db')).not.toThrow();
+  });
+});