style: 残片chip移除黄色竖条并补充业务定义悬浮提示

src/components/Welcome.vue

@@ -278,9 +278,16 @@ onBeforeUnmount(() => {
   <section class="welcome-page">
     <div class="review-scroll-section surface-card">
       <div class="review-scroll-header">
-        <span class="color-legend">
+        <el-tooltip
+          effect="dark"
+          placement="left"
+          :show-after="200"
+          content="学习残片（知识碎片）是学习过程中随手记下的不完整内容，不要求是完整总结，只记录刚学到、想到或需要记住的内容。它是学习记录的主要单元，后续由你或 AI 汇总为学习报告与思维导图。"
+        >
+          <span class="color-legend" tabindex="0">
             <span class="dot dot-fragment"></span> 学习残片
           </span>
+        </el-tooltip>
       </div>
       <div
         ref="trackRef"
@@ -450,6 +457,8 @@ onBeforeUnmount(() => {
   display: inline-flex;
   align-items: center;
   gap: 12px;
+  cursor: help;
+  outline: none;
 }
 
 .dot {
@@ -485,7 +494,6 @@ onBeforeUnmount(() => {
   padding: 8px 16px;
   background: var(--surface-strong);
   border: 1px solid var(--border-soft);
-  border-left: 3px solid var(--accent-warning);
   border-radius: 6px;
   cursor: pointer;
   transition: background 0.2s, box-shadow 0.2s;
@@ -495,7 +503,7 @@ onBeforeUnmount(() => {
 
 .review-chip:hover {
   box-shadow: var(--shadow-soft);
-  background: var(--accent-warning-soft);
+  background: var(--accent-success-softer);
 }
 
 .chip-task {