fix: 品牌设置tab中文化、保存提示、上传压缩优化

- Brand → 我的品牌, Account → 我的账户
- 保存品牌设置时显示"已保存" toast
- 图片压缩: 先试PNG，超限再降JPEG质量，缩小到600px
- 上传过程中显示"正在上传..."
- 失败显示具体错误信息

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

frontend/src/views/MyDiary.vue

@@ -2,8 +2,8 @@
   <div class="my-diary">
     <!-- Sub Tabs -->
     <div class="sub-tabs">
-      <button class="sub-tab" :class="{ active: activeTab === 'brand' }" @click="activeTab = 'brand'">🏷️ Brand</button>
-      <button class="sub-tab" :class="{ active: activeTab === 'account' }" @click="activeTab = 'account'">👤 Account</button>
+      <button class="sub-tab" :class="{ active: activeTab === 'brand' }" @click="activeTab = 'brand'">🏷 我的品牌</button>
+      <button class="sub-tab" :class="{ active: activeTab === 'account' }" @click="activeTab = 'account'">👤 我的账户</button>
     </div>
 
     <!-- Diary Tab -->
@@ -400,15 +400,16 @@ async function loadBrandSettings() {
 
 async function saveBrandSettings() {
   try {
-    await api('/api/brand', {
+    const res = await api('/api/brand', {
       method: 'PUT',
       body: JSON.stringify({
         brand_name: brandName.value,
         brand_align: brandAlign.value,
       }),
     })
+    if (res.ok) ui.showToast('已保存')
   } catch {
-    // silent
+    ui.showToast('保存失败')
   }
 }
 
@@ -427,7 +428,7 @@ function readFileAsBase64(file) {
   })
 }
 
-// Compress image if too large
+// Compress image if too large (keeps PNG for small images, JPEG for large)
 function compressImage(base64, maxSize = 500000) {
   return new Promise((resolve) => {
     if (base64.length <= maxSize) { resolve(base64); return }
@@ -435,8 +436,7 @@ function compressImage(base64, maxSize = 500000) {
     img.onload = () => {
       const canvas = document.createElement('canvas')
       let w = img.width, h = img.height
-      // Scale down if very large
-      const maxDim = 800
+      const maxDim = 600
       if (w > maxDim || h > maxDim) {
         const ratio = Math.min(maxDim / w, maxDim / h)
         w = Math.round(w * ratio)
@@ -445,14 +445,19 @@ function compressImage(base64, maxSize = 500000) {
       canvas.width = w
       canvas.height = h
       canvas.getContext('2d').drawImage(img, 0, 0, w, h)
-      let quality = 0.8
-      let result = canvas.toDataURL('image/jpeg', quality)
-      while (result.length > maxSize && quality > 0.2) {
-        quality -= 0.1
-        result = canvas.toDataURL('image/jpeg', quality)
+      // Try PNG first, then JPEG with decreasing quality
+      let result = canvas.toDataURL('image/png')
+      if (result.length > maxSize) {
+        let quality = 0.85
+        while (quality > 0.2) {
+          result = canvas.toDataURL('image/jpeg', quality)
+          if (result.length <= maxSize) break
+          quality -= 0.1
+        }
       }
       resolve(result)
     }
+    img.onerror = () => resolve(base64) // fallback: return original
     img.src = base64
   })
 }
@@ -467,6 +472,7 @@ async function handleUpload(type, event) {
     const fieldMap = { logo: 'brand_logo', bg: 'brand_bg', qr: 'qr_code' }
     const field = fieldMap[type]
     if (!field) return
+    ui.showToast('正在上传...')
     const res = await api('/api/brand', {
       method: 'PUT',
       body: JSON.stringify({ [field]: base64 }),
@@ -475,13 +481,13 @@ async function handleUpload(type, event) {
       if (type === 'logo') brandLogo.value = base64
       else if (type === 'bg') brandBg.value = base64
       else if (type === 'qr') brandQrImage.value = base64
-      ui.showToast('上传成功')
+      ui.showToast('上传成功 ✓')
     } else {
       const err = await res.json().catch(() => ({}))
-      ui.showToast(err.detail || '上传失败')
+      ui.showToast('上传失败: ' + (err.detail || res.status))
     }
   } catch (e) {
-    ui.showToast('上传失败: ' + (e.message || ''))
+    ui.showToast('上传出错: ' + (e.message || '网络错误'))
   }
   // Reset input so same file can be re-selected
   event.target.value = ''