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.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'
+}