fix: 上传图片保持比例、QR正方形裁剪、Logo左下角、日期靠右

上传图片:
- object-fit: contain 保持原比例，不压扁不拉长
- QR上传检测是否正方形，非正方形提示并自动裁剪中心区域

配方卡片:
- Logo位置改为左下角 (left:24px)
- 制作日期靠右对齐 (text-align:right)

品牌预览:
- Logo位置改为左下角 (left:16px)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/RecipeDetailOverlay.vue

@@ -1170,8 +1170,7 @@ async function saveRecipe() {
 .card-logo {
   position: absolute;
   bottom: 60px;
-  left: 50%;
-  transform: translateX(-50%);
+  left: 24px;
   height: 60px;
   object-fit: contain;
   z-index: 1;
@@ -1300,7 +1299,7 @@ async function saveRecipe() {
 
 .card-footer {
   margin-top: 16px;
-  text-align: center;
+  text-align: right;
   font-size: 11px;
   color: var(--text-light, #9a8570);
   letter-spacing: 1px;

frontend/src/views/MyDiary.vue

@@ -462,11 +462,56 @@ function compressImage(base64, maxSize = 500000) {
   })
 }
 
+// Crop image to square from center
+function cropToSquare(base64) {
+  return new Promise((resolve) => {
+    const img = new Image()
+    img.onload = () => {
+      const size = Math.min(img.width, img.height)
+      const x = (img.width - size) / 2
+      const y = (img.height - size) / 2
+      const canvas = document.createElement('canvas')
+      canvas.width = size
+      canvas.height = size
+      canvas.getContext('2d').drawImage(img, x, y, size, size, 0, 0, size, size)
+      resolve(canvas.toDataURL('image/png'))
+    }
+    img.onerror = () => resolve(base64)
+    img.src = base64
+  })
+}
+
+// Check if image is roughly square
+function checkSquare(base64) {
+  return new Promise((resolve) => {
+    const img = new Image()
+    img.onload = () => {
+      const ratio = img.width / img.height
+      resolve(ratio > 0.85 && ratio < 1.15) // within 15% of square
+    }
+    img.onerror = () => resolve(true)
+    img.src = base64
+  })
+}
+
 async function handleUpload(type, event) {
   const file = event.target.files[0]
   if (!file) return
   try {
     let base64 = await readFileAsBase64(file)
+
+    // QR: check if square, offer to crop
+    if (type === 'qr') {
+      const isSquare = await checkSquare(base64)
+      if (!isSquare) {
+        const { showConfirm: confirm } = await import('../composables/useDialog')
+        const ok = await confirm('二维码图片不是正方形，是否自动裁剪为正方形？\n（取中心区域）')
+        if (ok) {
+          base64 = await cropToSquare(base64)
+        }
+      }
+    }
+
     const maxSize = type === 'bg' ? 1000000 : 500000
     base64 = await compressImage(base64, maxSize)
     const fieldMap = { logo: 'brand_logo', bg: 'brand_bg', qr: 'qr_code' }
@@ -958,7 +1003,7 @@ async function applyBusiness() {
   transition: border-color 0.15s;
 }
 .upload-box:hover { border-color: var(--sage, #7a9e7e); }
-.upload-box-img { width: 100%; height: 100%; object-fit: cover; }
+.upload-box-img { width: 100%; height: 100%; object-fit: contain; }
 .upload-box-hint { font-size: 12px; color: var(--text-light, #9a8570); }
 .btn-clear {
   margin-top: 6px;
@@ -1019,8 +1064,7 @@ async function applyBusiness() {
 .card-preview-logo {
   position: absolute;
   bottom: 40px;
-  left: 50%;
-  transform: translateX(-50%);
+  left: 16px;
   height: 20px;
   width: auto;
   object-fit: contain;