fix(web): 修复 chat 来源在移动端横向溢出 + 向量索引 tab 加可选说明

- ChatSources: 来源链接 max-width 由固定 32rem 改为 100% 并加 min-width:0，
  容器补 min-width:0/max-width:100%，超长来源显示省略号，不再撑破窄屏导致整页横滚
- 向量索引设置 tab 顶部新增（可选）说明，提示不配置也能正常对话（zh/en/ja/de 四语）

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: lin-snow

web/src/locales/messages/de-DE.json

@@ -991,6 +991,7 @@
   },
   "embeddingSetting": {
     "title": "Vektorindex",
+    "optionalHint": "(Optional) Der Vektorindex ermöglicht Copilot die semantische Suche in deinen bisherigen Echos. Der Chat funktioniert auch ohne ihn.",
     "enable": "Index aktivieren",
     "modelName": "Embedding-Modell",
     "modelPlaceholder": "z. B. text-embedding-3-small",

web/src/locales/messages/en-US.json

@@ -991,6 +991,7 @@
   },
   "embeddingSetting": {
     "title": "Vector Index",
+    "optionalHint": "(Optional) The vector index lets Copilot semantically retrieve your past echos. Chat works fine without it.",
     "enable": "Enable index",
     "modelName": "Embedding model",
     "modelPlaceholder": "e.g. text-embedding-3-small",

web/src/locales/messages/ja-JP.json

@@ -991,6 +991,7 @@
   },
   "embeddingSetting": {
     "title": "ベクトルインデックス",
+    "optionalHint": "（任意）ベクトルインデックスは Copilot が過去の Echo を意味的に検索するための機能です。設定しなくても会話は利用できます。",
     "enable": "インデックスを有効化",
     "modelName": "Embedding モデル",
     "modelPlaceholder": "例: text-embedding-3-small",

web/src/locales/messages/zh-CN.json

@@ -991,6 +991,7 @@
   },
   "embeddingSetting": {
     "title": "向量索引",
+    "optionalHint": "（可选）向量索引用于让 Copilot 检索历史 Echo 的语义内容，不配置也能正常对话。",
     "enable": "启用索引",
     "modelName": "Embedding 模型",
     "modelPlaceholder": "如 text-embedding-3-small",

web/src/views/chat/modules/ChatSources.vue

@@ -112,12 +112,16 @@ const hiddenCount = computed(() => displaySources.value.length - LIMIT)
   flex-direction: column;
   gap: 0.15rem;
   margin-top: 0.35rem;
+  min-width: 0;
+  max-width: 100%;
 }
 
 .sources__item {
   display: flex;
   flex-direction: column;
   gap: 0.25rem;
+  min-width: 0;
+  max-width: 100%;
 }
 
 /* 缩略图行：紧贴来源文字下方，一排小图 */
@@ -158,7 +162,10 @@ const hiddenCount = computed(() => displaySources.value.length - LIMIT)
   display: inline-flex;
   align-items: baseline;
   gap: 0.3rem;
-  max-width: 32rem;
+
+  /* 用 100% 而非固定 32rem，避免在移动端窄屏下撑破容器导致整页横向滚动 */
+  max-width: 100%;
+  min-width: 0;
   border: none;
   background: transparent;
   padding: 0;

web/src/views/panel/modules/TheCopilot/TheEmbeddingSetting.vue

@@ -2,6 +2,9 @@
 <!-- Copyright (C) 2025-2026 lin-snow -->
 <template>
   <div class="w-full text-[var(--color-text-secondary)]">
+    <!-- 可选说明：向量索引非必需，不配置也能正常对话 -->
+    <p class="text-xs opacity-70 mb-4">{{ t('embeddingSetting.optionalHint') }}</p>
+
     <!-- 启用 -->
     <div class="flex items-center justify-between mb-4">
       <h2 class="font-semibold">{{ t('embeddingSetting.enable') }}</h2>