feat(exif): write the Xiaomi watermark blob (0x889e) so HyperOS Gallery can frame our captures

HyperOS Gallery reads EXIF 0x889e (a JSON blob) to build its watermark
frame; without it a photo fails with "cannot recognize the parameters".
CameraX/HAL never supplies that vendor tag, so a capture from this app
lacked it while a stock-camera photo carried it.

Read back the same props the stock camera derives the blob from
(ro.product.device / ro.product.marketname / Build.MANUFACTURER) via the
native module, synthesize the blob in exifWrite, and write it only when
the source has none and the device is Xiaomi/Redmi/POCO - a source blob
is never overwritten.

src/utils/photoMeta.ts

@@ -2,7 +2,8 @@
 // EXIF helpers both export engines share (the codec itself lives in exifWrite.ts).
 import { File } from 'expo-file-system';
 import * as FileSystem from 'expo-file-system/legacy';
-import { writeJpegExif, SOFTWARE, type ExifStamp } from './exifWrite';
+import RecipescamExport from '../../modules/recipescam-export';
+import { writeJpegExif, SOFTWARE, type DeviceIdentity, type ExifStamp } from './exifWrite';
 
 // RC_<yyyymmdd_hhmmss>[_exported].jpg — the name the gallery shows for a saved
 // photo. The exported variant marks a photo re-exported from the library.
@@ -33,6 +34,22 @@ export async function readPhotoBytes(uri: string): Promise<Uint8Array | null> {
   }
 }
 
+// Device identity for the Gallery watermark blob (exifWrite.watermarkBlob).
+// Read once — the props cannot change while the app runs. null when the native
+// module is older than this call, so stamping still works without it.
+let deviceIdentity: DeviceIdentity | null | undefined;
+export function getDeviceIdentity(): DeviceIdentity | null {
+  if (deviceIdentity === undefined) {
+    try {
+      deviceIdentity = RecipescamExport.deviceInfo();
+    } catch (e) {
+      console.warn('deviceInfo unavailable:', e);
+      deviceIdentity = null;
+    }
+  }
+  return deviceIdentity;
+}
+
 // Stamp EXIF into a file already on disk (the native engine writes the JPEG
 // itself, so those bytes never pass through JS). Never throws — a metadata
 // failure must not cost the user the photo.
@@ -40,7 +57,7 @@ export async function stampExifOnFile(fileUri: string, stamp: ExifStamp, sourceU
   try {
     const target = new File(fileUri);
     const source = sourceUri ? await readPhotoBytes(sourceUri) : null;
-    target.write(writeJpegExif(await target.bytes(), { software: SOFTWARE, ...stamp }, source));
+    target.write(writeJpegExif(await target.bytes(), { software: SOFTWARE, device: getDeviceIdentity(), ...stamp }, source));
   } catch (e) {
     console.warn('EXIF stamp failed:', e);
   }