QR upload: replace inline hint with dialog, add back button in brand page

- Replace the inline brand-upload-hint bar in RecipeDetailOverlay with a
  confirm dialog (「去上传」/「取消」) that pops up when the card opens
- Extend useDialog/CustomDialog to support custom ok/cancel button text
- Add a 「← 返回配方卡片」banner in MyDiary brand tab when navigated
  from a recipe card, allowing return without uploading

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/CustomDialog.vue

@@ -11,8 +11,8 @@
         ref="promptInput"
       />
       <div class="dialog-btn-row">
-        <button v-if="dialogState.type !== 'alert'" class="dialog-btn-outline" @click="cancel">取消</button>
-        <button class="dialog-btn-primary" @click="ok">确定</button>
+        <button v-if="dialogState.type !== 'alert'" class="dialog-btn-outline" @click="cancel">{{ dialogState.cancelText || '取消' }}</button>
+        <button class="dialog-btn-primary" @click="ok">{{ dialogState.okText || '确定' }}</button>
       </div>
     </div>
   </div>