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>

.ai/examples/good-api.json

@@ -0,0 +1,25 @@
+{
+  "success_example": {
+    "code": 0,
+    "message": "success",
+    "data": {
+      "summary": "简版结论占位",
+      "profile_id": "p_123"
+    }
+  },
+  "error_example": {
+    "code": 30001,
+    "message": "invalid birth date"
+  },
+  "list_example": {
+    "code": 0,
+    "message": "success",
+    "data": {
+      "list": [{ "slug": "mbti", "name": "MBTI" }],
+      "total": 1,
+      "page": 1,
+      "page_size": 20
+    }
+  },
+  "_comment": "Never use {success:true} or {ok:true} as root."
+}

.ai/examples/good-handler.go

@@ -0,0 +1,54 @@
+//go:build ignore
+
+// EXAMPLE — reference shape for AI. Not compiled into apps/api.
+package examples
+
+import (
+	"context"
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+)
+
+type apiBody struct {
+	Code    int         `json:"code"`
+	Message string      `json:"message"`
+	Data    interface{} `json:"data,omitempty"`
+}
+
+type DecodeInput struct {
+	Year  int
+	Month int
+	Day   int
+}
+
+type DecodeOutput struct {
+	Summary string `json:"summary"`
+}
+
+type DecodeService interface {
+	Decode(ctx context.Context, in DecodeInput) (*DecodeOutput, error)
+}
+
+type DecodeHandler struct {
+	Svc DecodeService
+}
+
+// Decode handles POST /api/v1/reports/decode
+func (h *DecodeHandler) Decode(c *gin.Context) {
+	var req struct {
+		Year  int `json:"year" binding:"required"`
+		Month int `json:"month" binding:"required"`
+		Day   int `json:"day" binding:"required"`
+	}
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, apiBody{Code: 10000, Message: "invalid request"})
+		return
+	}
+	out, err := h.Svc.Decode(c.Request.Context(), DecodeInput(req))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, apiBody{Code: 30001, Message: err.Error()})
+		return
+	}
+	c.JSON(http.StatusOK, apiBody{Code: 0, Message: "success", Data: out})
+}

.ai/examples/good-service.go

@@ -0,0 +1,29 @@
+//go:build ignore
+
+// EXAMPLE — reference shape for AI. Not compiled into apps/api.
+package examples
+
+import (
+	"context"
+	"fmt"
+)
+
+type DecodeRepo interface {
+	SaveDecode(ctx context.Context, userID string, summary string) error
+}
+
+type DecodeServiceImpl struct {
+	Repo DecodeRepo
+}
+
+func (s *DecodeServiceImpl) Decode(ctx context.Context, in DecodeInput) (*DecodeOutput, error) {
+	if in.Year < 1900 || in.Month < 1 || in.Month > 12 || in.Day < 1 || in.Day > 31 {
+		return nil, fmt.Errorf("invalid birth date")
+	}
+	// engine would run here
+	summary := "简版结论占位"
+	if err := s.Repo.SaveDecode(ctx, "user-from-ctx", summary); err != nil {
+		return nil, fmt.Errorf("save decode: %w", err)
+	}
+	return &DecodeOutput{Summary: summary}, nil
+}

.ai/examples/good-test.go

@@ -0,0 +1,39 @@
+//go:build ignore
+
+// EXAMPLE — table-driven unit test shape.
+package examples
+
+import "testing"
+
+func TestClampBirthMonth(t *testing.T) {
+	tests := []struct {
+		name    string
+		month   int
+		wantErr bool
+	}{
+		{name: "ok", month: 6, wantErr: false},
+		{name: "zero", month: 0, wantErr: true},
+		{name: "thirteen", month: 13, wantErr: true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := validateMonth(tt.month)
+			if (err != nil) != tt.wantErr {
+				t.Fatalf("validateMonth(%d) err=%v wantErr=%v", tt.month, err, tt.wantErr)
+			}
+		})
+	}
+}
+
+func validateMonth(m int) error {
+	if m < 1 || m > 12 {
+		return errInvalid
+	}
+	return nil
+}
+
+var errInvalid = errString("invalid")
+
+type errString string
+
+func (e errString) Error() string { return string(e) }