fix: 调研/产品/UI 实际耗时改为精确时间戳显示和计算

- PlanTab 自动进入"进行中"时调用 onUpdate 记录 actualStartAt
- 显示实际开始时间和完成时间（精确到分钟）
- calcPlanDuration 改为用时间差计算小时数（精确到0.5h）
- formatDuration 显示小时而非天数

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

apps/web/components/version/PlanTab.tsx

@@ -55,13 +55,20 @@ export function PlanTab({ plans, versionId, versionDeadline, currentUserName, pl
       ) : (
         <div className="space-y-3">
           {typePlans.map((plan) => {
-            // 已耗时：已完成用实际完成时间，进行中用当前时间，未开始为0
-            const now = new Date().toISOString().slice(0, 10);
-            const effectiveStatus = plan.status === 'pending' && plan.startTime <= now ? 'in_progress' : plan.status;
-            const dur = effectiveStatus === 'completed' && plan.completedAt
-              ? calcPlanDuration(plan.startTime, plan.completedAt)
-              : effectiveStatus === 'in_progress'
-                ? calcPlanDuration(plan.startTime, now)
+            const now = new Date().toISOString();
+            const nowDate = now.slice(0, 10);
+            // 自动进入进行中（到了计划开始日期）
+            const shouldAutoStart = plan.status === 'pending' && plan.startTime <= nowDate;
+            if (shouldAutoStart && !plan.actualStartAt) {
+              onUpdate(plan.id, { status: 'in_progress' });
+            }
+            const effectiveStatus = shouldAutoStart ? 'in_progress' : plan.status;
+            // 耗时用实际时间戳计算
+            const actualStart = plan.actualStartAt || (shouldAutoStart ? now : null);
+            const dur = effectiveStatus === 'completed' && plan.completedAt && actualStart
+              ? calcPlanDuration(actualStart, plan.completedAt)
+              : effectiveStatus === 'in_progress' && actualStart
+                ? calcPlanDuration(actualStart, now)
                 : { days: 0, hours: 0 };
             const durText = dur.days > 0 || dur.hours > 0 ? formatDuration(dur.days, dur.hours) : '-';
             return (
@@ -76,7 +83,8 @@ export function PlanTab({ plans, versionId, versionDeadline, currentUserName, pl
                     </div>
                     <div className="flex items-center gap-4 text-[12px] text-[var(--ink-soft)]">
                       <span>计划：{plan.startTime.slice(0, 10)} → {plan.endTime.slice(0, 10)}</span>
-                      {plan.completedAt && <span className="text-green-600">完成：{plan.completedAt.slice(0, 10)}</span>}
+                      {plan.actualStartAt && <span className="text-blue-600">实际开始：{plan.actualStartAt.slice(0, 16).replace('T', ' ')}</span>}
+                      {plan.completedAt && <span className="text-green-600">完成：{plan.completedAt.slice(0, 16).replace('T', ' ')}</span>}
                       <span className="font-medium text-[var(--ink)]">已耗时 {durText}</span>
                     </div>
                     {plan.overdueReason && (