fix(photos): shared EXIF-oriented decode for axis/overlay space (#72)

PhotoStage used new Image() while mask worker and calculate used bare
createImageBitmap; Orientation-8 matched-set JPEGs can disagree across
those paths so the approved pink axis is not the overlay (ux,uy).

One decodeOrientedBitmap helper always requests imageOrientation
from-image (with bare fallback), wired into PhotoStage, mask.worker,
and session calculate/siblings.

frontend/src/worker/mask.worker.ts

@@ -1,5 +1,6 @@
 import { minAreaRect, slabBounds } from '../geometry/rect';
 import type { MaskParams, WorkerIn, WorkerOut } from '../capture/capture.types';
+import { decodeOrientedBitmap } from '../decodeOrientedBitmap';
 
 let bitmap: ImageBitmap | null = null;
 let data: Uint8ClampedArray | null = null;
@@ -69,7 +70,7 @@ self.onmessage = (e: MessageEvent<WorkerIn>) => {
     }
     data = null;
     w = h = 0;
-    createImageBitmap(msg.blob)
+    decodeOrientedBitmap(msg.blob)
       .then((bmp) => {
         w = bmp.width;
         h = bmp.height;