重构: 前端God文件拆分(StreamRenderer+EmptyState+MentionPopover+EnrichmentPanel)

- useStreamRenderer.ts: 流式Markdown块级渲染提取为composable(220行)

- EmptyState.vue: 空状态独立组件(无provider引导+示例问题)

- MentionPopover.vue: @实体联想浮层独立组件

- EnrichmentPanel.vue: @项目enrichment预览面板独立组件

- MessageList.vue: 1386→1148行, ChatInput.vue: 1155→1007行

- AiChat进度条: completedTools计数器(AiToolCallCompleted+1,AiAgentRound重置)

- i18n: 进度条文案加已完成工具数(中英文)

src/i18n/en/ai.ts

@@ -45,6 +45,6 @@ export default {
     // Note: max round / completed tool count are not surfaced by backend this round;
     // template conditionally omits them. Add *WithMax keys once backend exposes them.
     agenticProgress: '🔄 Round {round} · ⏳{pending} pending',
-    agenticProgressNoPending: '🔄 Round {round}',
+    agenticProgressNoPending: '🔄 Round {round} · ✅{completed} tools done',
   },
 }