test(api): Work-sessions — fill gaps + lifecycle test

Drives src/routes/sessions.ts and src/lib/work-session.ts to 100%
stmts/branch/funcs/lines (branch was 84.12% / 83.33%).

- sessions.test.ts: added error/edge branch tests — malformed-JSON start
  (400), non-numeric id on pause/resume/stop/discard (404), pause/resume of a
  no-longer-active session (409), discard missing (404) + already-closed (409),
  stop missing (404), and discard ownership scoping (user B → 404).
- work-session.test.ts: mapper unit tests — null insoleType, nullish
  pausedSeconds → 0, null durationSeconds/notes, full-field shape with
  activity/user opts, and opts defaulting to undefined.
- test/integration/worker-session-lifecycle.test.ts: the anchor lifecycle test
  (start→pause→resume→stop→history→export).

No bugs found — the code was correct. The two remaining uncovered branches were
the defensive `row.pausedSeconds ?? 0` guards in resume/stop; pausedSeconds is
NOT NULL DEFAULT 0 in the schema, so the null branch is unreachable via any
route. Annotated both with `/* c8 ignore next -- reason */` (comment only, no
behavior change).

apps/api/test/work-session.test.ts

@@ -37,3 +37,71 @@ describe('toWorkSession paused fields', () => {
     expect(result.paused_at).toBe(pausedAt.toISOString());
   });
 });
+
+describe('toWorkSession field mapping', () => {
+  it('maps a null insoleType to null', () => {
+    const result = toWorkSession(baseRow({ insoleType: null }));
+    expect(result.insole_type).toBeNull();
+  });
+
+  it('coalesces a nullish pausedSeconds to 0 (defensive against a null column value)', () => {
+    const result = toWorkSession(baseRow({ pausedSeconds: null as unknown as number }));
+    expect(result.paused_seconds).toBe(0);
+  });
+
+  it('coalesces a nullish durationSeconds to null and a nullish notes to null', () => {
+    const result = toWorkSession(baseRow({ durationSeconds: null, notes: null }));
+    expect(result.duration_seconds).toBeNull();
+    expect(result.notes).toBeNull();
+  });
+
+  it('shapes every field, threading activity/user opts through', () => {
+    const start = new Date('2026-06-17T08:00:00.000Z');
+    const end = new Date('2026-06-17T09:30:00.000Z');
+    const created = new Date('2026-06-17T07:59:00.000Z');
+    const result = toWorkSession(
+      baseRow({
+        id: 42,
+        userId: 'user-42',
+        activityId: 7,
+        insoleType: 'Berk',
+        pairCount: 4,
+        startTime: start,
+        endTime: end,
+        durationSeconds: 5000,
+        pausedSeconds: 400,
+        status: 'completed',
+        source: 'manual',
+        notes: 'handmatig',
+        createdAt: created,
+      }),
+      { activityName: 'Frezen', userName: 'Jan', userEmail: 'jan@example.com' },
+    );
+    expect(result).toEqual({
+      id: 42,
+      user_id: 'user-42',
+      activity_id: 7,
+      activity_name: 'Frezen',
+      user_name: 'Jan',
+      user_email: 'jan@example.com',
+      insole_type: 'Berk',
+      pair_count: 4,
+      start_time: start.toISOString(),
+      end_time: end.toISOString(),
+      duration_seconds: 5000,
+      paused_seconds: 400,
+      paused_at: null,
+      status: 'completed',
+      source: 'manual',
+      notes: 'handmatig',
+      created_at: created.toISOString(),
+    });
+  });
+
+  it('defaults activity/user opts to undefined when omitted', () => {
+    const result = toWorkSession(baseRow());
+    expect(result.activity_name).toBeUndefined();
+    expect(result.user_name).toBeUndefined();
+    expect(result.user_email).toBeUndefined();
+  });
+});