add unit test suite: 80 tests across utils, api, auth, clients, events, emails

- Vitest + React Testing Library + jsdom setup
- utils.test.ts: cn, formatDate, formatFullDate, getInitials, getRelativeTime, getDaysUntil
- api.test.ts: token management, auth, CRUD for clients/events/emails, admin, error handling
- auth.test.ts: login, logout, checkSession, setUser
- clients.test.ts: fetch, create, update, delete, markContacted, filters
- events.test.ts: fetch, create, update, delete, syncAll
- emails.test.ts: fetch, generate, update, send, delete

src/lib/utils.test.ts

@@ -0,0 +1,140 @@
+import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest';
+import { cn, formatDate, formatFullDate, getInitials, getRelativeTime, getDaysUntil } from './utils';
+
+describe('cn', () => {
+  it('merges class names', () => {
+    expect(cn('foo', 'bar')).toBe('foo bar');
+  });
+
+  it('handles conditional classes', () => {
+    expect(cn('base', false && 'hidden', 'visible')).toBe('base visible');
+  });
+
+  it('merges tailwind conflicts', () => {
+    expect(cn('px-4', 'px-2')).toBe('px-2');
+  });
+});
+
+describe('formatDate', () => {
+  beforeEach(() => {
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date('2026-01-28T12:00:00Z'));
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it('returns empty string for undefined', () => {
+    expect(formatDate(undefined)).toBe('');
+  });
+
+  it('returns "Today" for today\'s date', () => {
+    expect(formatDate('2026-01-28')).toBe('Today');
+  });
+
+  it('returns "Tomorrow" for tomorrow\'s date', () => {
+    expect(formatDate('2026-01-29')).toBe('Tomorrow');
+  });
+
+  it('returns "Yesterday" for yesterday\'s date', () => {
+    expect(formatDate('2026-01-27')).toBe('Yesterday');
+  });
+
+  it('returns short format for same year', () => {
+    const result = formatDate('2026-03-15');
+    expect(result).toBe('Mar 15');
+  });
+
+  it('returns full format for different year', () => {
+    const result = formatDate('2025-03-15');
+    expect(result).toBe('Mar 15, 2025');
+  });
+});
+
+describe('formatFullDate', () => {
+  it('returns empty string for undefined', () => {
+    expect(formatFullDate(undefined)).toBe('');
+  });
+
+  it('returns full formatted date', () => {
+    const result = formatFullDate('2026-01-28');
+    expect(result).toContain('January');
+    expect(result).toContain('28');
+    expect(result).toContain('2026');
+  });
+});
+
+describe('getInitials', () => {
+  it('returns initials from first and last name', () => {
+    expect(getInitials('John', 'Doe')).toBe('JD');
+  });
+
+  it('handles empty strings', () => {
+    expect(getInitials('', '')).toBe('');
+  });
+
+  it('handles single name', () => {
+    expect(getInitials('Alice', '')).toBe('A');
+  });
+});
+
+describe('getRelativeTime', () => {
+  beforeEach(() => {
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date('2026-01-28T12:00:00Z'));
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it('returns "Never" for undefined', () => {
+    expect(getRelativeTime(undefined)).toBe('Never');
+  });
+
+  it('returns "Today" for today', () => {
+    expect(getRelativeTime('2026-01-28T10:00:00Z')).toBe('Today');
+  });
+
+  it('returns "Yesterday" for yesterday', () => {
+    expect(getRelativeTime('2026-01-27T10:00:00Z')).toBe('Yesterday');
+  });
+
+  it('returns days ago for recent dates', () => {
+    expect(getRelativeTime('2026-01-25T10:00:00Z')).toBe('3 days ago');
+  });
+
+  it('returns weeks ago', () => {
+    expect(getRelativeTime('2026-01-14T10:00:00Z')).toBe('2 weeks ago');
+  });
+
+  it('returns months ago', () => {
+    expect(getRelativeTime('2025-11-28T10:00:00Z')).toBe('2 months ago');
+  });
+});
+
+describe('getDaysUntil', () => {
+  beforeEach(() => {
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date('2026-01-28T12:00:00Z'));
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it('returns 0 for today', () => {
+    expect(getDaysUntil('2026-01-28')).toBe(0);
+  });
+
+  it('returns positive for future dates', () => {
+    expect(getDaysUntil('2026-02-01')).toBe(4);
+  });
+
+  it('projects past dates to next occurrence', () => {
+    // Jan 15 already passed, should project to next year
+    const days = getDaysUntil('2025-01-15');
+    expect(days).toBeGreaterThan(300); // ~352 days to Jan 15 2027
+  });
+});