feat(mobile): track mobile app scaffold

mobile/app/src/platform/README.md

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+# Platform Layer
+
+平台能力统一放在本目录，页面不直接绑定具体 Expo/原生库。
+
+- `camera`：相机、相册、票据采集和本地预处理。
+- `voice`：录音、语音转写、麦克风权限。
+- `upload`：附件上传、进度、重试、临时附件引用。
+- `permissions`：Android / iOS 权限文案和降级策略。
+
+相机与语音都先产生用户可确认的中间结果，不直接触发草稿持久化或提交审批。

mobile/app/src/platform/camera/receiptCapture.ts

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+import * as ImagePicker from 'expo-image-picker';
+
+export type CapturedReceipt = {
+  uri: string;
+  fileName: string;
+  mimeType?: string;
+  source: 'camera' | 'library';
+};
+
+function toReceipt(asset: ImagePicker.ImagePickerAsset, source: CapturedReceipt['source']): CapturedReceipt {
+  return {
+    uri: asset.uri,
+    fileName: asset.fileName || `receipt-${Date.now()}.jpg`,
+    mimeType: asset.mimeType,
+    source,
+  };
+}
+
+export async function captureReceiptFromCamera(): Promise<CapturedReceipt | null> {
+  const permission = await ImagePicker.requestCameraPermissionsAsync();
+  if (!permission.granted) {
+    throw new Error('需要相机权限才能拍摄票据。');
+  }
+
+  const result = await ImagePicker.launchCameraAsync({
+    allowsEditing: false,
+    quality: 0.84,
+    mediaTypes: ['images'],
+  });
+
+  if (result.canceled || !result.assets[0]) {
+    return null;
+  }
+
+  return toReceipt(result.assets[0], 'camera');
+}
+
+export async function pickReceiptFromLibrary(): Promise<CapturedReceipt | null> {
+  const permission = await ImagePicker.requestMediaLibraryPermissionsAsync();
+  if (!permission.granted) {
+    throw new Error('需要相册权限才能选择票据图片。');
+  }
+
+  const result = await ImagePicker.launchImageLibraryAsync({
+    allowsEditing: false,
+    quality: 0.88,
+    mediaTypes: ['images'],
+  });
+
+  if (result.canceled || !result.assets[0]) {
+    return null;
+  }
+
+  return toReceipt(result.assets[0], 'library');
+}

mobile/app/src/platform/voice/voiceInput.ts

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+import { useAudioRecorder, RecordingPresets } from 'expo-audio';
+
+export function useVoiceRecorder() {
+  const recorder = useAudioRecorder(RecordingPresets.HIGH_QUALITY);
+
+  return {
+    recorder,
+    async start() {
+      await recorder.prepareToRecordAsync();
+      recorder.record();
+    },
+    async stop() {
+      await recorder.stop();
+      return recorder.uri;
+    },
+  };
+}
+
+export async function transcribeVoice(uri: string) {
+  // 后续接入 /api/v1/mobile/voice/transcribe；初始化阶段先返回可见占位结果。
+  return {
+    text: `已收到语音文件：${uri.split('/').pop() || 'voice-recording'}`,
+    confidence: 0,
+  };
+}