DNG/RAW photo support for gallery upload

- Server: accept .dng in OCR endpoint (PIL opens as TIFF)
- Server: bump OCR size limit to 20MB (DNG files can be large)
- Client: gallery upload tries server OCR first (with 6s timeout),
  then falls back to client-side Tesseract.js — matches 📸 capture flow
- DNG photos now work with 'Pick from Gallery'

server.py

@@ -2629,12 +2629,12 @@ async def ocr_sticker(file: UploadFile = File(...)):
     """
     # Validate file extension
     ext = file.filename.rsplit(".", 1)[-1].lower() if "." in (file.filename or "") else ""
-    if ext not in {"png", "jpg", "jpeg", "webp", "bmp"}:
+    if ext not in {"png", "jpg", "jpeg", "webp", "bmp", "dng"}:
         raise HTTPException(status_code=400, detail=f"Unsupported image format: .{ext}")
 
     contents = await file.read()
-    if len(contents) > 10 * 1024 * 1024:  # 10MB max
-        raise HTTPException(status_code=400, detail="Image too large (max 10MB)")
+    if len(contents) > 20 * 1024 * 1024:  # 20MB max
+        raise HTTPException(status_code=400, detail="Image too large (max 20MB)")
 
     # Save temp file for OCR
     temp_dir = Path(UPLOADS_DIR / "ocr")