test(api): Worker export/CSV — fill gaps + lifecycle test

Drove src/lib/csv.ts to 100% stmts/branch/funcs/lines (was 97.95%/55.55%):
- added a null-fallback row test covering every ?? default (activityName,
  userName, insoleType→Kurk, pairCount→2, duration/paused→0) and the null
  end-time branch (line 65).
- added CSV-escaping edge tests: commas, embedded quotes, and newlines inside
  a field stay inside the quoted cell.
- added formatDuration edge (hours >99 → 100:00:00).
- added a /api/export ordering-by-start-time behavior test and adopted
  resetDb per-test isolation in the export suite.

No bugs found; CSV code behaves correctly. sessions.ts /api/export route
already at 100%. Full api suite green (150 tests).

apps/api/test/export.test.ts

@@ -1,11 +1,11 @@
-import { describe, it, expect } from 'vitest';
+import { describe, it, expect, beforeEach } from 'vitest';
 import type { Hono } from 'hono';
 import { createApp } from '../src/app';
 import { db } from '../src/db/client';
 import { workSessions } from '../src/db/schema';
 import { eq } from 'drizzle-orm';
 import { quote, formatDuration } from '../src/lib/csv';
-import { authToken, bearer, seedActivity } from './helpers';
+import { authToken, bearer, seedActivity, resetDb } from './helpers';
 
 // Start a session, backdate its start_time by `durationSeconds`, then stop it,
 // producing a completed session with an exact duration.
@@ -31,6 +31,8 @@ async function completedSession(
 }
 
 describe('csv export', () => {
+  beforeEach(resetDb);
+
   it('401s without a token', async () => {
     const app = createApp();
     const res = await app.request('/api/export');
@@ -118,6 +120,32 @@ describe('csv export', () => {
     const lines = (await res.text()).split('\n');
     expect(lines).toHaveLength(2); // header + 1 completed row
   });
+
+  it('orders rows by start time ascending', async () => {
+    const app = createApp();
+    const token = await authToken(app, 'export-order@example.com');
+    const frezenId = await seedActivity('Frezen');
+    const slijpenId = await seedActivity('Slijpen');
+
+    // Two completed sessions; make Frezen clearly the older start.
+    const older = await completedSession(app, token, frezenId, 'Kurk', 30);
+    const newer = await completedSession(app, token, slijpenId, 'Berk', 30);
+    await db
+      .update(workSessions)
+      .set({ startTime: new Date(Date.now() - 60000) })
+      .where(eq(workSessions.id, older));
+    await db
+      .update(workSessions)
+      .set({ startTime: new Date(Date.now() - 10000) })
+      .where(eq(workSessions.id, newer));
+
+    const lines = (
+      await (await app.request('/api/export', { headers: bearer(token) })).text()
+    ).split('\n');
+    expect(lines).toHaveLength(3); // header + 2 rows
+    expect(lines[1]).toContain('"Frezen"'); // oldest start first
+    expect(lines[2]).toContain('"Slijpen"');
+  });
 });
 
 describe('csv helpers', () => {