fix(fe): canvas fallback for decodeOrientedBitmap when createImageBitmap is absent

The LAN dev URL is a non-secure, sometimes restricted browser where
createImageBitmap may be undefined; the pick-calibration -> mask decode
would then reject. Fall back to a canvas + Image decode returning an
ImageBitmap. Contract unchanged (still returns ImageBitmap).

frontend/src/capture/decodeOrientedBitmap.ts

@@ -4,17 +4,19 @@
  *
  * Matched-set / DJI JPEGs often carry EXIF Orientation 8 (stored landscape,
  * display portrait). `new Image()` and bare `createImageBitmap(blob)` can
- * disagree across browsers → axis arrow space ≠ mask bitset space.
+ * disagree across browsers -> axis arrow space != mask bitset space.
  *
- * Contract: always request `imageOrientation: 'from-image'`. If the runtime
- * rejects that option (older engines), fall back to bare `createImageBitmap`;
- * engines that already apply EXIF by default still match Image/canvas size.
+ * Contract: always request `imageOrientation: 'from-image'` when supported.
+ * The dev environment is LAN-HTTP (a non-secure, sometimes restricted
+ * browser) where `createImageBitmap` may be absent, so fall back to a
+ * canvas + Image decode that returns an ImageBitmap.
  */
 export const ORIENTED_BITMAP_OPTIONS: ImageBitmapOptions = {
   imageOrientation: 'from-image',
 };
 
 export async function decodeOrientedBitmap(blob: Blob): Promise<ImageBitmap> {
+  if (typeof createImageBitmap === 'function') {
     try {
       return await createImageBitmap(blob, ORIENTED_BITMAP_OPTIONS);
     } catch (first) {
@@ -25,3 +27,31 @@ export async function decodeOrientedBitmap(blob: Blob): Promise<ImageBitmap> {
       }
     }
   }
+  return decodeViaCanvas(blob);
+}
+
+/** Canvas + Image decode for engines without createImageBitmap. */
+async function decodeViaCanvas(blob: Blob): Promise<ImageBitmap> {
+  const url = URL.createObjectURL(blob);
+  try {
+    const img = await loadImage(url);
+    const canvas = document.createElement('canvas');
+    canvas.width = img.naturalWidth;
+    canvas.height = img.naturalHeight;
+    const ctx = canvas.getContext('2d', { willReadFrequently: true });
+    if (!ctx) throw new Error('2d context unavailable');
+    ctx.drawImage(img, 0, 0);
+    return await createImageBitmap(canvas);
+  } finally {
+    URL.revokeObjectURL(url);
+  }
+}
+
+function loadImage(url: string): Promise<HTMLImageElement> {
+  return new Promise((resolve, reject) => {
+    const img = new Image();
+    img.onload = () => resolve(img);
+    img.onerror = () => reject(new Error('image decode failed'));
+    img.src = url;
+  });
+}