fix: Logo提示语改为'卡片左下角水印'，Logo清晰显示(opacity:1)

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

frontend/src/components/RecipeDetailOverlay.vue

@@ -1165,7 +1165,7 @@ async function saveRecipe() {
 .ec-logo {
   height: 36px;
   object-fit: contain;
-  opacity: 0.5;
+  opacity: 1;
 }
 .ec-date {
   font-size: 11px;

frontend/src/views/MyDiary.vue

@@ -144,7 +144,7 @@
           <!-- Logo -->
           <div>
             <label class="form-label">🏷 Logo</label>
-            <p style="font-size:11px;color:var(--text-light);margin-bottom:6px">卡片底部居中水印</p>
+            <p style="font-size:11px;color:var(--text-light);margin-bottom:6px">卡片左下角水印</p>
             <div class="upload-box" @click="triggerUpload('logo')">
               <img v-if="brandLogo" :src="brandLogo" class="upload-box-img" />
               <span v-else class="upload-box-hint">点击上传</span>
@@ -190,7 +190,7 @@
               </div>
               <!-- Logo left + Date right -->
               <div style="display:flex;justify-content:space-between;align-items:flex-end;margin-top:8px">
-                <img v-if="brandLogo" :src="brandLogo" style="height:18px;object-fit:contain;opacity:0.5" />
+                <img v-if="brandLogo" :src="brandLogo" style="height:18px;object-fit:contain" />
                 <span v-else></span>
                 <span style="font-size:7px;color:var(--text-light);letter-spacing:0.5px">制作日期：{{ new Date().toLocaleDateString('zh-CN') }}</span>
               </div>