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/composables/useDialog.js

@@ -5,6 +5,8 @@ export const dialogState = reactive({
   type: 'alert', // 'alert', 'confirm', 'prompt'
   message: '',
   defaultValue: '',
+  okText: '',
+  cancelText: '',
   resolve: null
 })
 
@@ -13,15 +15,19 @@ export function showAlert(msg) {
     dialogState.visible = true
     dialogState.type = 'alert'
     dialogState.message = msg
+    dialogState.okText = ''
+    dialogState.cancelText = ''
     dialogState.resolve = resolve
   })
 }
 
-export function showConfirm(msg) {
+export function showConfirm(msg, opts = {}) {
   return new Promise(resolve => {
     dialogState.visible = true
     dialogState.type = 'confirm'
     dialogState.message = msg
+    dialogState.okText = opts.okText || ''
+    dialogState.cancelText = opts.cancelText || ''
     dialogState.resolve = resolve
   })
 }