优化: 无障碍第二批(icon-only aria-label + 容器键盘化 20 处)

- TopBar 10 处 icon-only 按钮补 aria-label(复用同 :title 表达式,含三态 title)
- ConversationSidebar: 4 icon-only aria-label + 2 分组标题键盘化(role/tabindex/aria-expanded/keydown)
- MessageList 2 icon-only; KnowledgeDetail 3 章节折叠键盘化; dashboard 两列表项键盘化
- FileExplorer 面包屑/模块下拉项键盘化; ConflictResolver 冲突文件折叠键盘化
- 约定: 遮罩/点外关闭类(@click.self)非键盘缺口,跳过;零新增 i18n 键
- 验收: bunx vue-tsc --noEmit EXIT 0;看板 P3-2 更新(两批共 23 处)

src/components/project/FileExplorer.vue

@@ -20,13 +20,24 @@
               :key="m.id"
               class="module-dropdown-item"
               :class="{ active: m.id === currentModuleId }"
+              role="button"
+              tabindex="0"
               @click="onModuleSelect(m.id)"
+              @keydown.enter.prevent="onModuleSelect(m.id)"
+              @keydown.space.prevent="onModuleSelect(m.id)"
             >
               <span class="module-dropdown-name">{{ m.name }}</span>
               <span v-if="m.path" class="module-dropdown-path" :title="m.path">{{ m.path }}</span>
             </div>
             <div class="module-dropdown-divider"></div>
-            <div class="module-dropdown-item module-dropdown-action" @click="onScanSubmodules">
+            <div
+              class="module-dropdown-item module-dropdown-action"
+              role="button"
+              tabindex="0"
+              @click="onScanSubmodules"
+              @keydown.enter.prevent="onScanSubmodules"
+              @keydown.space.prevent="onScanSubmodules"
+            >
               <span class="module-dropdown-name">🔍 {{ $t('fileExplorer.scanSubmodules') }}</span>
             </div>
           </div>
@@ -34,12 +45,27 @@
 
         <!-- 路径面包屑 -->
         <nav class="breadcrumb">
-          <span class="crumb crumb-root" :title="currentModule?.path ?? ''" @click="goRoot">
+          <span
+            class="crumb crumb-root"
+            :title="currentModule?.path ?? ''"
+            role="button"
+            tabindex="0"
+            @click="goRoot"
+            @keydown.enter.prevent="goRoot"
+            @keydown.space.prevent="goRoot"
+          >
             {{ currentModule?.name ?? '...' }}
           </span>
           <template v-for="(seg, idx) in breadcrumbSegments" :key="idx">
             <span class="crumb-sep">/</span>
-            <span class="crumb" @click="goBreadcrumb(seg.path)">{{ seg.name }}</span>
+            <span
+              class="crumb"
+              role="button"
+              tabindex="0"
+              @click="goBreadcrumb(seg.path)"
+              @keydown.enter.prevent="goBreadcrumb(seg.path)"
+              @keydown.space.prevent="goBreadcrumb(seg.path)"
+            >{{ seg.name }}</span>
           </template>
         </nav>
       </div>