fix(live-log): Fehlermeldung wenn keine Systemkamera vorhanden ist

Prüft videoinput-Geräte beim Öffnen des Foto-Modals und zeigt eine
klare Meldung statt leerem Kamera-UI; getUserMedia-Fehler differenziert.

Co-authored-by: Cursor <cursoragent@cursor.com>

client/src/utils/cameraAvailability.test.ts

@@ -0,0 +1,47 @@
+import { describe, expect, it, vi } from 'vitest'
+import {
+  cameraErrorKeyFromDomException,
+  isCameraApiSupported,
+  probeCameraAvailability
+} from './cameraAvailability.js'
+
+describe('cameraAvailability', () => {
+  it('detects missing camera API', () => {
+    const nav = { mediaDevices: undefined }
+    vi.stubGlobal('navigator', nav)
+    expect(isCameraApiSupported()).toBe(false)
+    vi.unstubAllGlobals()
+  })
+
+  it('returns none when no videoinput devices', async () => {
+    vi.stubGlobal('navigator', {
+      mediaDevices: {
+        getUserMedia: vi.fn(),
+        enumerateDevices: vi.fn().mockResolvedValue([
+          { kind: 'audioinput', deviceId: 'a1', label: '', groupId: '' }
+        ])
+      }
+    })
+    await expect(probeCameraAvailability()).resolves.toBe('none')
+    vi.unstubAllGlobals()
+  })
+
+  it('returns available when a videoinput exists', async () => {
+    vi.stubGlobal('navigator', {
+      mediaDevices: {
+        getUserMedia: vi.fn(),
+        enumerateDevices: vi.fn().mockResolvedValue([
+          { kind: 'videoinput', deviceId: 'v1', label: '', groupId: '' }
+        ])
+      }
+    })
+    await expect(probeCameraAvailability()).resolves.toBe('available')
+    vi.unstubAllGlobals()
+  })
+
+  it('maps NotFoundError to no-camera i18n key', () => {
+    expect(cameraErrorKeyFromDomException(new DOMException('', 'NotFoundError'))).toBe(
+      'logs.live_photo_no_camera'
+    )
+  })
+})

client/src/utils/cameraAvailability.ts

@@ -0,0 +1,33 @@
+export type CameraAvailability = 'available' | 'none' | 'unsupported'
+
+/** Whether the browser exposes camera APIs at all. */
+export function isCameraApiSupported(): boolean {
+  return typeof navigator !== 'undefined' && !!navigator.mediaDevices?.getUserMedia
+}
+
+/** Best-effort probe for at least one video input device (no permission prompt). */
+export async function probeCameraAvailability(): Promise<CameraAvailability> {
+  if (!isCameraApiSupported()) return 'unsupported'
+  if (!navigator.mediaDevices?.enumerateDevices) {
+    // Cannot list devices; defer to getUserMedia attempt in the capture UI.
+    return 'available'
+  }
+  try {
+    const devices = await navigator.mediaDevices.enumerateDevices()
+    if (devices.some((d) => d.kind === 'videoinput')) return 'available'
+    return 'none'
+  } catch {
+    return 'none'
+  }
+}
+
+export function cameraErrorKeyFromDomException(err: unknown): string {
+  const name = err instanceof DOMException ? err.name : ''
+  if (name === 'NotFoundError' || name === 'OverconstrainedError') {
+    return 'logs.live_photo_no_camera'
+  }
+  if (name === 'NotAllowedError' || name === 'NotReadableError' || name === 'SecurityError') {
+    return 'logs.live_photo_camera_denied'
+  }
+  return 'logs.live_photo_camera_unavailable'
+}