feat(server-go): 蚕房健康画像与年度发病统计（#24）

server-go/internal/handler/trace.go

@@ -20,6 +20,7 @@ func RegisterTraceRoutes(rg *gin.RouterGroup, db *gorm.DB) {
 	write := middleware.RequirePermission(db, "trace:write")
 	rg.GET("/trace-records", read, listTraceRecords(db))
 	rg.GET("/trace-records/region-stats", read, traceRegionStats(db))
+	rg.GET("/trace-records/monthly-stats", read, traceMonthlyStats(db))
 	rg.GET("/trace-records/:id", read, getTraceRecord(db))
 	rg.POST("/trace-records", write, createTraceRecord(db))
 	rg.PATCH("/trace-records/:id", write, updateTraceRecord(db))
@@ -29,6 +30,31 @@ func RegisterTraceRoutes(rg *gin.RouterGroup, db *gorm.DB) {
 	rg.POST("/trace-records/:id/checklist", write, submitTraceChecklist(db))
 }
 
+// traceMonthlyStats 年度发病规律（按月聚合）
+func traceMonthlyStats(db *gorm.DB) gin.HandlerFunc {
+	return func(c *gin.Context) {
+		year := time.Now().Year()
+		if y, err := strconv.Atoi(c.DefaultQuery("year", "0")); err == nil && y >= 2020 && y <= 2100 {
+			year = y
+		}
+		start := time.Date(year, 1, 1, 0, 0, 0, 0, time.Local)
+		end := start.AddDate(1, 0, 0)
+		var rows []struct {
+			Month   string `gorm:"column:month"`
+			Disease string `gorm:"column:disease"`
+		}
+		db.Table("trace_records").
+			Select("to_char(created_at, 'YYYY-MM') AS month, disease").
+			Where("created_at >= ? AND created_at < ?", start, end).
+			Scan(&rows)
+		entries := make([]service.MonthDiseaseEntry, 0, len(rows))
+		for _, r := range rows {
+			entries = append(entries, service.MonthDiseaseEntry{Month: r.Month, Disease: r.Disease})
+		}
+		c.JSON(http.StatusOK, gin.H{"year": year, "stats": service.AggregateMonthlyStats(entries)})
+	}
+}
+
 // traceRegionStats 区域发病统计（近 N 天，按蚕房 region 聚合）
 func traceRegionStats(db *gorm.DB) gin.HandlerFunc {
 	return func(c *gin.Context) {