test: add comprehensive test suite (115 tests, Vitest + supertest + nock)

Framework:
- Vitest v4 as test runner (fast ESM/CJS support, V8 coverage built-in)
- supertest for integration tests against createApp() factory
- nock for HTTP interception (works with CJS require('axios'), unlike vi.mock)

New files:
- vitest.config.js          — test config: node env, isolate, V8 coverage, per-file thresholds
- tests/setup.js             — isolated DATA_DIR per worker, SKIP_RATE_LIMIT, console suppression
- tests/README.md            — approach, structure, design decisions
- server/app.js              — testable Express factory (extracted from index.js side-effects)

Unit tests (91 tests):
- tests/unit/sanitizeError.test.js  — secret redaction: apikey, token, bearer, basic-auth URLs
- tests/unit/config.test.js         — JSON array + legacy single-instance config parsing
- tests/unit/requireAuth.test.js    — valid/invalid/tampered cookies, schema validation
- tests/unit/verifyCsrf.test.js     — double-submit pattern, timing-safe compare, safe methods
- tests/unit/qbittorrent.test.js    — formatBytes, formatEta, mapTorrentToDownload state map
- tests/unit/tokenStore.test.js     — store/get/clear lifecycle, TTL expiry, atomic disk write

Integration tests (24 tests):
- tests/integration/health.test.js  — /health and /ready endpoints
- tests/integration/auth.test.js    — full login/logout/me/csrf flows, input validation,
                                      cookie attributes, no token leakage, Emby mock via nock

Production code changes (minimal, no behaviour change):
- server/routes/auth.js: EMBY_URL captured at request-time (not module load) for testability
- server/routes/auth.js: loginLimiter max → Number.MAX_SAFE_INTEGER when SKIP_RATE_LIMIT set
- server/utils/sanitizeError.js: fix HEADER_PATTERN to redact full line (not just first token)

CI:
- .gitea/workflows/ci.yml: add parallel 'test' job (npm run test:coverage, artifact upload)
- package.json: add test/test:watch/test:coverage/test:ui scripts
- .gitignore: add coverage/

tests/unit/qbittorrent.test.js

@@ -0,0 +1,111 @@
+/**
+ * Tests for server/utils/qbittorrent.js pure utility functions.
+ *
+ * mapTorrentToDownload, formatBytes, formatSpeed, and formatEta are all
+ * pure functions with no I/O — ideal unit test targets. These power the
+ * dashboard card rendering so correctness matters for UX.
+ */
+
+import { mapTorrentToDownload, formatBytes, formatSpeed, formatEta } from '../../server/utils/qbittorrent.js';
+
+// Minimal torrent fixture that satisfies mapTorrentToDownload's expectations
+function makeTorrent(overrides = {}) {
+  return {
+    name: 'My.Show.S01E01.1080p.mkv',
+    state: 'downloading',
+    size: 1073741824,        // 1 GB
+    completed: 536870912,    // 512 MB
+    progress: 0.5,
+    dlspeed: 1048576,        // 1 MB/s
+    eta: 512,                // seconds
+    num_seeds: 10,
+    num_leechs: 3,
+    availability: 1.0,
+    hash: 'aabbccdd',
+    category: 'sonarr',
+    tags: '',
+    content_path: '/downloads/My.Show.S01E01.1080p.mkv',
+    save_path: '/downloads/',
+    instanceName: 'i3omb',
+    ...overrides
+  };
+}
+
+describe('formatBytes', () => {
+  it('formats 0 bytes', () => expect(formatBytes(0)).toBe('0 B'));
+  it('formats bytes', () => expect(formatBytes(512)).toBe('512 B'));
+  it('formats kilobytes', () => expect(formatBytes(1024)).toBe('1 KB'));
+  it('formats megabytes', () => expect(formatBytes(1048576)).toBe('1 MB'));
+  it('formats gigabytes', () => expect(formatBytes(1073741824)).toBe('1 GB'));
+  it('formats fractional GB', () => expect(formatBytes(1610612736)).toBe('1.5 GB'));
+});
+
+describe('formatSpeed', () => {
+  it('appends /s to byte count', () => expect(formatSpeed(1048576)).toBe('1 MB/s'));
+  it('handles zero speed', () => expect(formatSpeed(0)).toBe('0 B/s'));
+});
+
+describe('formatEta', () => {
+  it('returns ∞ for qBittorrent unknown sentinel (8640000)', () => {
+    expect(formatEta(8640000)).toBe('∞');
+  });
+  it('returns ∞ for negative eta', () => expect(formatEta(-1)).toBe('∞'));
+  it('formats minutes only', () => expect(formatEta(90)).toBe('1m'));
+  it('formats hours and minutes', () => expect(formatEta(3661)).toBe('1h 1m'));
+  it('formats days, hours and minutes', () => expect(formatEta(90061)).toBe('1d 1h 1m'));
+  it('returns 0m for zero seconds', () => expect(formatEta(0)).toBe('0m'));
+});
+
+describe('mapTorrentToDownload', () => {
+  it('maps a downloading torrent correctly', () => {
+    const result = mapTorrentToDownload(makeTorrent());
+    expect(result.status).toBe('Downloading');
+    expect(result.progress).toBe('50.0');
+    expect(result.size).toBe('1 GB');
+    expect(result.speed).toBe('1 MB/s');
+    expect(result.eta).toBe('8m');
+    expect(result.seeds).toBe(10);
+    expect(result.peers).toBe(3);
+    expect(result.qbittorrent).toBe(true);
+    expect(result.instanceName).toBe('i3omb');
+  });
+
+  it('maps state: stalledDL → Downloading', () => {
+    expect(mapTorrentToDownload(makeTorrent({ state: 'stalledDL' })).status).toBe('Downloading');
+  });
+
+  it('maps state: uploading → Seeding', () => {
+    expect(mapTorrentToDownload(makeTorrent({ state: 'uploading' })).status).toBe('Seeding');
+  });
+
+  it('maps state: pausedDL → Paused', () => {
+    expect(mapTorrentToDownload(makeTorrent({ state: 'pausedDL' })).status).toBe('Paused');
+  });
+
+  it('maps state: stoppedUP → Stopped', () => {
+    expect(mapTorrentToDownload(makeTorrent({ state: 'stoppedUP' })).status).toBe('Stopped');
+  });
+
+  it('maps state: error → Error', () => {
+    expect(mapTorrentToDownload(makeTorrent({ state: 'error' })).status).toBe('Error');
+  });
+
+  it('passes through unknown state verbatim', () => {
+    expect(mapTorrentToDownload(makeTorrent({ state: 'weirdState' })).status).toBe('weirdState');
+  });
+
+  it('computes 100% progress for completed torrent', () => {
+    const result = mapTorrentToDownload(makeTorrent({ progress: 1.0 }));
+    expect(result.progress).toBe('100.0');
+  });
+
+  it('uses content_path as savePath when present', () => {
+    const result = mapTorrentToDownload(makeTorrent({ content_path: '/dl/file.mkv' }));
+    expect(result.savePath).toBe('/dl/file.mkv');
+  });
+
+  it('falls back to save_path when content_path is absent', () => {
+    const result = mapTorrentToDownload(makeTorrent({ content_path: null, save_path: '/dl/' }));
+    expect(result.savePath).toBe('/dl/');
+  });
+});