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/capture/session.ts

@@ -10,6 +10,7 @@ import { measure } from '../measure/measure';
 import { orientedRect } from '../geometry/rect';
 import { encodeInventoryPng, type InventoryInput } from '../png/inventory';
 import { encodeOverlayPng, type EncodeOverlayInput } from '../png/overlay';
+import { decodeOrientedBitmap } from '../decodeOrientedBitmap';
 
 const DEBOUNCE_MS = 2000;
 const BUSY_MS = 300;
@@ -512,7 +513,7 @@ export function createCaptureSession(opts: SessionOpts = {}): CaptureSession {
       if (state.k !== 'measure') return;
       const { source, approvedMask, axis, lengthEighths, thicknessEighths } = state;
       if (lengthEighths === 0 || thicknessEighths === 0) return;
-      const bitmap = await createImageBitmap(source.blob);
+      const bitmap = await decodeOrientedBitmap(source.blob);
       const base = measure(
         approvedMask.bitset, source.widthPx, source.heightPx,
         axis.bbox, lengthEighths, thicknessEighths, approvedMask.slabPx,
@@ -587,7 +588,7 @@ export function createCaptureSession(opts: SessionOpts = {}): CaptureSession {
             widthPx: derived.widthPx,
             heightPx: derived.heightPx,
           };
-          const siblingBitmap = await createImageBitmap(photo.blob);
+          const siblingBitmap = await decodeOrientedBitmap(photo.blob);
           let encoded: { blob: Blob; sourceBelowFloor: boolean };
           try {
             encoded = await encodeInventory({ bitmap: siblingBitmap, mask: derived.mask, source: siblingSource });