feat: #67 GET /activity/trend 新增 dailySeries 时间序列数据

返回格式新增 dailySeries 字段 [{date, value, label}]，支持 iOS 折线图/柱状图渲染。
数据来源：按日聚合 LearningActivity.durationSeconds。

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/modules/ai/prompts/schemas/learning-trend.schema.ts

@@ -8,6 +8,12 @@ export const TrendItemSchema = z.object({
   detail: z.string().max(500),
 });
 
+export const DailySeriesItemSchema = z.object({
+  date: z.string(),
+  value: z.number(),
+  label: z.string(),
+});
+
 export const LearningTrendResultSchema = z.object({
   periodSummary: z.string().min(1).max(2000),
   overallScore: z.number().int().min(0).max(100),
@@ -17,9 +23,11 @@ export const LearningTrendResultSchema = z.object({
   weaknesses: z.array(z.string().max(500)).max(10).default([]),
   recommendations: z.array(z.string().max(500)).max(10).default([]),
   nextFocusAreas: z.array(z.string().max(200)).max(5).default([]),
+  dailySeries: z.array(DailySeriesItemSchema).default([]),
 });
 
 export type LearningTrendResult = z.infer<typeof LearningTrendResultSchema>;
+export type DailySeriesItem = z.infer<typeof DailySeriesItemSchema>;
 
 export const LEARNING_TREND_OUTPUT_SCHEMA_DESC = `{
   "periodSummary": "过去7天，你的学习时长为320分钟，完成了45次主动回忆和120张复习卡片。整体掌握水平有所提升。",

src/modules/learning-activity/learning-activity.service.ts

@@ -66,6 +66,9 @@ export class LearningActivityService {
 
     const prevTotalMinutes = Math.round(sum(previous, 'durationSeconds') / 60);
 
+    // Build daily time-series for chart rendering
+    const dailySeries = this.buildDailySeries(recent, periodDays);
+
     const trendInput = {
       userId,
       periodDays,
@@ -86,6 +89,28 @@ export class LearningActivityService {
       } : undefined,
     };
 
-    return this.trendWorkflow.execute(trendInput);
+    const aiResult = await this.trendWorkflow.execute(trendInput);
+    return { ...aiResult, dailySeries };
+  }
+
+  private buildDailySeries(activities: any[], days: number) {
+    const series: { date: string; value: number; label: string }[] = [];
+    const now = new Date();
+    for (let i = days - 1; i >= 0; i--) {
+      const d = new Date(now);
+      d.setDate(d.getDate() - i);
+      const dateStr = d.toISOString().split('T')[0];
+      const dayActs = activities.filter((a) => {
+        const ad = a.activityDate instanceof Date ? a.activityDate : new Date(a.activityDate);
+        return ad.toISOString().split('T')[0] === dateStr;
+      });
+      const minutes = Math.round(dayActs.reduce((s: number, a: any) => s + a.durationSeconds, 0) / 60);
+      series.push({
+        date: dateStr,
+        value: minutes,
+        label: `${minutes}分钟`,
+      });
+    }
+    return series;
   }
 }