chore: seal Design Vision v1 and monorepo scaffold

Archive the differentiated YuXinGu product docs, AI engineering system,
design contract, and Go/Vue scaffold. Next execution prioritizes Cece-parity
over early innovation (see .ai/product/STRATEGY.md).

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/api/cmd/server/main.go

@@ -0,0 +1,39 @@
+// Command server starts the 愈心谷 HTTP API.
+package main
+
+import (
+	"log"
+	"os"
+
+	"github.com/gin-gonic/gin"
+
+	"github.com/yuxingu/digital-psychology/apps/api/internal/config"
+	"github.com/yuxingu/digital-psychology/apps/api/internal/handler"
+	"github.com/yuxingu/digital-psychology/apps/api/internal/middleware"
+	"github.com/yuxingu/digital-psychology/apps/api/pkg/response"
+)
+
+func main() {
+	cfg := config.Load()
+	if cfg.AppEnv == "prod" {
+		gin.SetMode(gin.ReleaseMode)
+	}
+
+	r := gin.New()
+	r.Use(gin.Recovery(), gin.Logger(), middleware.RequestID())
+
+	api := r.Group("/api/v1")
+	handler.NewHealthHandler().Register(api)
+
+	// Placeholder route to demonstrate unified envelope.
+	api.GET("/ping", func(c *gin.Context) {
+		response.OK(c, gin.H{"pong": true})
+	})
+
+	addr := cfg.HTTPAddr
+	log.Printf("yuxingu api listening on %s env=%s", addr, cfg.AppEnv)
+	if err := r.Run(addr); err != nil {
+		log.Printf("server stopped: %v", err)
+		os.Exit(1)
+	}
+}