重构: 前端DRY收口+后端测试类型对齐

- 新增 useToast composable: 消除 AiChat/Settings/Projects 4处 toast 重复
  统一默认3000ms(Projects原4000ms为操作类提示保留参数覆盖)
- 新增 utils/json.ts parseJsonArray: 消除 parseStack/parseTags/ModuleNode
  3处JSON字符串数组解析重复
- 新增 utils/html.ts escapeHtml: 消除 useMarkdown/FilePreview 2处重复
- ProjectDetail score-bar 内联三元改用 scoreTier(消除最后一处阈值硬编码)
- ConversationSidebar 删除 formatTime 透传包装(直接用 formatRelative)
- 清理死代码: parseTs/stringifyError/ErrorSink/_Unused 改私有或删除
  wrapNakedDiff 改私有(无外部 import)
- ModuleNode shortPath 改名 truncatedPath(与 useToolCard.shortPath 语义不同)

src/components/ai/ConversationSidebar.vue

@@ -50,7 +50,7 @@
                 {{ conv.title || t('aiChat.newConversation') }}
                 <span v-if="store.isGenerating(conv.id)" class="ai-conv-gen-dot" :title="t('aiChat.generating')"></span>
               </span>
-              <span class="ai-conv-item-time">{{ formatTime(conv.updated_at) }}</span>
+              <span class="ai-conv-item-time">{{ formatRelative(conv.updated_at) }}</span>
             </div>
             <div class="ai-conv-item-actions">
               <div class="ai-conv-item-more">
@@ -132,7 +132,7 @@
                   <!-- F-09: 多会话并发生成指示器(后台/当前会话生成中均显脉冲点,多会话可同时显示) -->
                   <span v-if="store.isGenerating(conv.id)" class="ai-conv-gen-dot" :title="t('aiChat.generating')"></span>
                 </span>
-                <span class="ai-conv-item-time">{{ formatTime(conv.updated_at) }}</span>
+                <span class="ai-conv-item-time">{{ formatRelative(conv.updated_at) }}</span>
               </div>
               <div class="ai-conv-item-actions">
                 <div class="ai-conv-item-more">
@@ -177,7 +177,7 @@
                   {{ conv.title || t('aiChat.newConversation') }}
                   <span v-if="store.isGenerating(conv.id)" class="ai-conv-gen-dot" :title="t('aiChat.generating')"></span>
                 </span>
-                <span class="ai-conv-item-time">{{ formatTime(conv.updated_at) }}</span>
+                <span class="ai-conv-item-time">{{ formatRelative(conv.updated_at) }}</span>
               </div>
               <div class="ai-conv-item-actions">
                 <div class="ai-conv-item-more">
@@ -328,10 +328,6 @@ function onSelectSearchResult(id: string) {
   store.state.searchQuery = ''
 }
 
-function formatTime(ts: string): string {
-  return formatRelative(ts)
-}
-
 // ── 对话分组:今天 / 昨天 / 更早 ──
 const bucketLabels = computed<Record<string, string>>(() => ({
   today: t('aiChat.today'),