fix: 调研/产品/UI阶段耗时改为精确时间戳计算

- VersionPlan 新增 actualStartAt 字段
- updatePlan 流转到 in_progress 时自动记录 actualStartAt
- updatePlan 流转到 completed 时自动记录 completedAt（如未设）
- 概览阶段耗时改用 actualStartAt/completedAt 计算（不再用计划排期）
- 个人耗时汇总同步使用实际时间戳

所有阶段（调研/产品/UI/开发/测试）现在统一用精确时间戳算耗时。

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/stores/useVersionPlanStore.ts

@@ -43,7 +43,18 @@ export const useVersionPlanStore = create<VersionPlanState>((set, get) => ({
   },
 
   updatePlan: (id, data) => {
-    const plans = get().plans.map((p) => p.id === id ? { ...p, ...data } : p);
+    const now = new Date().toISOString();
+    const plans = get().plans.map((p) => {
+      if (p.id !== id) return p;
+      const patch = { ...data };
+      if (patch.status === 'in_progress' && !p.actualStartAt) {
+        (patch as any).actualStartAt = now;
+      }
+      if (patch.status === 'completed' && !p.completedAt) {
+        (patch as any).completedAt = now;
+      }
+      return { ...p, ...patch };
+    });
     set({ plans });
     saveLocal(plans);
   },