fix(mobile): use dynamic platform in feedback, add null coercion, add Content-Type on flush

- settings.tsx: replace hardcoded platform: 'ios' with APP_PLATFORM from app-metadata
- feedback-client.ts: add ?? '' null coercion on getAuthToken (matches broadcast/survey pattern)
- offline-queue.ts: add Content-Type: application/json header on flush requests

mobile/src/app/(tabs)/settings.tsx

@@ -3,6 +3,7 @@ import { Alert, Pressable, ScrollView, StyleSheet, Text, TextInput, View } from
 import { router } from 'expo-router';
 import { useAuthStore, type AuthState } from '../../store/auth-store';
 import { getFeedbackClient } from '../../lib/feedback-client';
+import { APP_PLATFORM } from '../../lib/app-metadata';
 import { colors } from '../../theme';
 
 type FeedbackType = 'bug' | 'feature' | 'praise' | 'other';
@@ -27,7 +28,7 @@ export default function SettingsScreen() {
         type: feedbackType,
         title,
         body: feedbackBody.trim() || undefined,
-        platform: 'ios',
+        platform: APP_PLATFORM,
       });
       setFeedbackTitle('');
       setFeedbackBody('');

mobile/src/lib/feedback-client.ts

@@ -8,7 +8,7 @@ export function getFeedbackClient(): FeedbackClient {
   if (!feedbackClient) {
     feedbackClient = createFeedbackClient({
       baseUrl: API_CONFIG.platformBaseUrl,
-      getAuthToken: () => getAuthClient().getAccessToken(),
+      getAuthToken: () => getAuthClient().getAccessToken() ?? '',
     });
   }
 

mobile/src/lib/offline-queue.ts

@@ -64,6 +64,7 @@ export async function flushNoteQueue(): Promise<{ flushed: number; failed: numbe
   return noteOfflineQueue.flush(async (action, path, payload) => {
     await getApiClient().fetch(path, {
       method: action === 'create' ? 'POST' : 'PATCH',
+      headers: { 'Content-Type': 'application/json' },
       body: JSON.stringify(payload),
     });
   });