fix: camera crash — add NSCameraUsageDescription + availability check

Crash: iOS terminates the app when accessing camera without the
privacy description in Info.plist.

Fix:
- Added NSCameraUsageDescription to Info.plist
- "Take Photo" option only shows if camera is available
  (UIImagePickerController.isSourceTypeAvailable(.camera))

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ios/Platform/Platform/Features/Assistant/AssistantChatView.swift

@@ -87,11 +87,13 @@ struct AssistantChatView: View {
             // Input bar
             HStack(alignment: .bottom, spacing: 10) {
                 Menu {
+                    if UIImagePickerController.isSourceTypeAvailable(.camera) {
                         Button {
                             showCamera = true
                         } label: {
                             Label("Take Photo", systemImage: "camera")
                         }
+                    }
 
                     Button {
                         showPhotoPicker = true

ios/Platform/Platform/Info.plist

@@ -6,5 +6,7 @@
 	<true/>
 	<key>ITSAppUsesNonExemptEncryption</key>
 	<false/>
+	<key>NSCameraUsageDescription</key>
+	<string>Take a photo of your meal to log it with AI</string>
 </dict>
 </plist>