Add comprehensive backend test suite (#339)

* add test suite, mostly covers integration testing, tests are only backend side

* workflow runs the correct script

* workflow runs the correct script

* workflow runs the correct script

* unit tests incoming

* Fix multer silent rejections and error handler info leak

- Revert cb(null, false) to cb(new Error(...)) in auth.ts, collab.ts,
  and files.ts so invalid uploads return an error instead of silently
  dropping the file
- Error handler in app.ts now always returns 500 / "Internal server
  error" instead of forwarding err.message to the client

* Use statusCode consistently for multer errors and error handler

- Error handler in app.ts reads err.statusCode to forward the correct
  HTTP status while keeping the response body generic

server/tests/unit/services/queryHelpers.test.ts

@@ -0,0 +1,123 @@
+import { describe, it, expect, vi } from 'vitest';
+
+vi.mock('../../../src/db/database', () => ({
+  db: { prepare: () => ({ all: () => [], get: vi.fn() }) },
+}));
+
+import { formatAssignmentWithPlace } from '../../../src/services/queryHelpers';
+import type { AssignmentRow, Tag, Participant } from '../../../src/types';
+
+function makeRow(overrides: Partial<AssignmentRow> = {}): AssignmentRow {
+  return {
+    id: 1,
+    day_id: 10,
+    place_id: 100,
+    order_index: 0,
+    notes: 'assignment note',
+    created_at: '2024-01-01T00:00:00Z',
+    place_name: 'Eiffel Tower',
+    place_description: 'Famous landmark',
+    lat: 48.8584,
+    lng: 2.2945,
+    address: 'Champ de Mars, Paris',
+    category_id: 5,
+    category_name: 'Sightseeing',
+    category_color: '#3b82f6',
+    category_icon: 'landmark',
+    price: 25.0,
+    place_currency: 'EUR',
+    place_time: '10:00',
+    end_time: '12:00',
+    duration_minutes: 120,
+    place_notes: 'Bring tickets',
+    image_url: 'https://example.com/img.jpg',
+    transport_mode: 'walk',
+    google_place_id: 'ChIJLU7jZClu5kcR4PcOOO6p3I0',
+    website: 'https://eiffel-tower.com',
+    phone: '+33 1 2345 6789',
+    ...overrides,
+  } as AssignmentRow;
+}
+
+const sampleTags: Partial<Tag>[] = [
+  { id: 1, name: 'Must-see', color: '#ef4444' },
+];
+
+const sampleParticipants: Participant[] = [
+  { user_id: 42, username: 'alice', avatar: null },
+];
+
+describe('formatAssignmentWithPlace', () => {
+  it('returns correct top-level shape', () => {
+    const result = formatAssignmentWithPlace(makeRow(), sampleTags, sampleParticipants);
+    expect(result).toHaveProperty('id', 1);
+    expect(result).toHaveProperty('day_id', 10);
+    expect(result).toHaveProperty('order_index', 0);
+    expect(result).toHaveProperty('notes', 'assignment note');
+    expect(result).toHaveProperty('created_at');
+    expect(result).toHaveProperty('place');
+    expect(result).toHaveProperty('participants');
+  });
+
+  it('nests place fields correctly from flat row', () => {
+    const result = formatAssignmentWithPlace(makeRow(), [], []);
+    const { place } = result;
+    expect(place.id).toBe(100);
+    expect(place.name).toBe('Eiffel Tower');
+    expect(place.description).toBe('Famous landmark');
+    expect(place.lat).toBe(48.8584);
+    expect(place.lng).toBe(2.2945);
+    expect(place.address).toBe('Champ de Mars, Paris');
+    expect(place.price).toBe(25.0);
+    expect(place.currency).toBe('EUR');
+    expect(place.place_time).toBe('10:00');
+    expect(place.end_time).toBe('12:00');
+    expect(place.duration_minutes).toBe(120);
+    expect(place.notes).toBe('Bring tickets');
+    expect(place.image_url).toBe('https://example.com/img.jpg');
+    expect(place.transport_mode).toBe('walk');
+    expect(place.google_place_id).toBe('ChIJLU7jZClu5kcR4PcOOO6p3I0');
+    expect(place.website).toBe('https://eiffel-tower.com');
+    expect(place.phone).toBe('+33 1 2345 6789');
+  });
+
+  it('constructs place.category object when category_id is present', () => {
+    const result = formatAssignmentWithPlace(makeRow(), [], []);
+    expect(result.place.category).toEqual({
+      id: 5,
+      name: 'Sightseeing',
+      color: '#3b82f6',
+      icon: 'landmark',
+    });
+  });
+
+  it('sets place.category to null when category_id is null', () => {
+    const result = formatAssignmentWithPlace(makeRow({ category_id: null as any }), [], []);
+    expect(result.place.category).toBeNull();
+  });
+
+  it('sets place.category to null when category_id is 0 (falsy)', () => {
+    const result = formatAssignmentWithPlace(makeRow({ category_id: 0 as any }), [], []);
+    expect(result.place.category).toBeNull();
+  });
+
+  it('includes provided tags in place.tags', () => {
+    const result = formatAssignmentWithPlace(makeRow(), sampleTags, []);
+    expect(result.place.tags).toEqual(sampleTags);
+  });
+
+  it('defaults place.tags to [] when empty array provided', () => {
+    const result = formatAssignmentWithPlace(makeRow(), [], []);
+    expect(result.place.tags).toEqual([]);
+  });
+
+  it('includes provided participants', () => {
+    const result = formatAssignmentWithPlace(makeRow(), [], sampleParticipants);
+    expect(result.participants).toEqual(sampleParticipants);
+  });
+
+  it('defaults participants to [] when empty array provided', () => {
+    const result = formatAssignmentWithPlace(makeRow(), [], []);
+    expect(result.participants).toEqual([]);
+  });
+});