fix: thread cropOrientation into StickerCanvas (was using device orientation)

StickerCanvas was being passed contextOrientation (the target device's
orientation), so the final composited.jpg was always sized to the device's
aspect — even when the user toggled the crop tool to a different orientation.
A landscape crop on a portrait device would produce a 1600x960 cropped
blob, then the StickerCanvas would re-render it into a 960x1600 frame,
visibly stretching the image into portrait dimensions and saving it that
way.

UploadView now derives an effectiveOrientation that prefers the user's
chosen crop orientation (uploadStore.cropOrientation) and falls back to
the device's orientation only before the crop step has run. The
StickerCanvas honors that.

Also adds a temporary debug log in the upload controller to verify the
cropOrientation form field is arriving and being persisted — recent
uploads have NULL cropOrientation despite the frontend sending it, and
this log will make the next upload's payload visible. Will remove once
diagnosed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/views/UploadView.vue

@@ -41,7 +41,7 @@
     <StickerCanvas
       v-else-if="step === 'stickers' && uploadStore.croppedUrl"
       :cropped-url="uploadStore.croppedUrl"
-      :orientation="contextOrientation"
+      :orientation="effectiveOrientation"
       :stickers="uploadStore.stickers"
       class="upload-view__stage"
       @add-sticker="uploadStore.addSticker"
@@ -124,6 +124,13 @@ const contextOrientation = computed<'landscape' | 'portrait'>(() =>
   contextDevice.value?.orientation ?? 'landscape'
 )
 
+// Once the user picks a crop orientation it drives the rest of the flow
+// (StickerCanvas aspect, output blob dims). Falls back to the device's
+// orientation while the crop step hasn't been completed yet.
+const effectiveOrientation = computed<'landscape' | 'portrait'>(() =>
+  uploadStore.cropOrientation ?? contextOrientation.value
+)
+
 const contextDeviceName = computed(() => contextDevice.value?.name)
 
 // ── Steps ─────────────────────────────────────────────────────────────────────