server OCR: accept any file extension, detect format from bytes

- Removed extension whitelist — no more 'unsupported format' errors
- Falls back to .jpg temp file for unknown/no extension
- PIL detects actual image format from file bytes (handles DNG as TIFF)
- Android browsers often strip DNG extensions when picking from gallery
- Tested: works with .dng, .jpg, no extension, and .bogus

server.py

@@ -2627,16 +2627,15 @@ async def ocr_sticker(file: UploadFile = File(...)):
     Accepts an image upload, runs Tesseract OCR, and looks for a pattern like
     '12345-678901'. Returns the extracted machine_id or an error.
     """
-    # 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", "dng"}:
-        raise HTTPException(status_code=400, detail=f"Unsupported image format: .{ext}")
-
+    # Read file contents first (validate size before saving)
     contents = await file.read()
     if len(contents) > 20 * 1024 * 1024:  # 20MB max
         raise HTTPException(status_code=400, detail="Image too large (max 20MB)")
 
-    # Save temp file for OCR
+    # Save temp file for OCR — try original extension, fallback to jpg
+    ext = file.filename.rsplit(".", 1)[-1].lower() if "." in (file.filename or "") else "jpg"
+    if ext not in {"png", "jpg", "jpeg", "webp", "bmp", "dng", "tiff", "tif"}:
+        ext = "jpg"  # PIL detects format from bytes regardless of extension
     temp_dir = Path(UPLOADS_DIR / "ocr")
     temp_dir.mkdir(parents=True, exist_ok=True)
     temp_path = temp_dir / f"{uuid.uuid4().hex}.{ext or 'jpg'}"