feat: 完善创作工作台与用户诊断支持 (#295)

* feat(canvas): 参考素材 - 增加移除按钮并删除对应连线

* feat(canvas): 完善节点面板交互与拖拽反馈

* fix(canvas): 画布交互与小地图 - 统一浮层层级并完善节点识别

* feat(prompt-optimizer): 增加 AI 提示词优化器及宿主接入

* feat(canvas): 画布 - 增加自动整理节点按钮并补充文档

* chore(web): 前端 - 修正提示词优化器格式

* chore(backend): 后端 - 修正 Go 格式检查

* feat(workspace): 完善诊断导出与本地排障支持

* chore(web): 格式化诊断导出文件

* fix(web-test): 兼容 Bun 测试运行时

* fix(web-test): 对齐模型目录协议断言

backend/internal/handler/diagnostics.go

@@ -0,0 +1,57 @@
+package handler
+
+import (
+	"fmt"
+	"net/http"
+
+	"infinite-canvas/backend/internal/service"
+
+	"github.com/gin-gonic/gin"
+)
+
+func RegisterDiagnosticsRoutes(r *gin.RouterGroup, svc *service.Service) {
+	r.POST("/diagnostics/preview", func(c *gin.Context) {
+		user, err := currentUser(c, svc)
+		if err != nil {
+			failService(c, err)
+			return
+		}
+		c.Request.Body = http.MaxBytesReader(c.Writer, c.Request.Body, 4<<20)
+		var req service.DiagnosticExportRequest
+		if err := c.ShouldBindJSON(&req); err != nil {
+			fail(c, http.StatusBadRequest, err)
+			return
+		}
+		preview, err := svc.PreviewDiagnosticBundle(user.ID, req)
+		if err != nil {
+			failService(c, err)
+			return
+		}
+		ok(c, preview)
+	})
+
+	r.POST("/diagnostics/export", func(c *gin.Context) {
+		user, err := currentUser(c, svc)
+		if err != nil {
+			failService(c, err)
+			return
+		}
+		c.Request.Body = http.MaxBytesReader(c.Writer, c.Request.Body, 4<<20)
+		var req service.DiagnosticExportRequest
+		if err := c.ShouldBindJSON(&req); err != nil {
+			fail(c, http.StatusBadRequest, err)
+			return
+		}
+		bundle, err := svc.ExportDiagnosticBundle(user.ID, req)
+		if err != nil {
+			failService(c, err)
+			return
+		}
+		c.Header("Cache-Control", "private, no-store")
+		c.Header("Content-Disposition", fmt.Sprintf("attachment; filename=%q", bundle.FileName))
+		c.Header("X-Diagnostic-Bundle-ID", bundle.BundleID)
+		c.Header("X-Diagnostic-Schema-Version", "1")
+		c.Data(http.StatusOK, "application/zip", bundle.Data)
+	})
+
+}