refactor: reorganize models to pkg/model and add authentication module

- Move ORM models from internal/model to pkg/model organized by module (auth/k8s/registry)
- Add authentication module with login, user management handlers
- Update all import paths to use new model locations
- Add frontend auth pages (Login, UserManagement) and authStore
- Remove deprecated internal/model/model.go

pkg/model/auth/user.go

@@ -0,0 +1,23 @@
+package auth
+
+import (
+	"time"
+
+	"gorm.io/gorm"
+)
+
+// User 用户模型
+type User struct {
+	ID        uint           `gorm:"primarykey" json:"id"`
+	CreatedAt time.Time      `json:"created_at"`
+	UpdatedAt time.Time      `json:"updated_at"`
+	DeletedAt gorm.DeletedAt `gorm:"index" json:"-"`
+
+	Username    string `gorm:"uniqueIndex;not null" json:"username"`
+	Password    string `gorm:"not null" json:"-"`
+	Email       string `gorm:"index" json:"email"`
+	Nickname    string `json:"nickname"`
+	Role        string `gorm:"default:'user'" json:"role"`
+	Status      string `gorm:"default:'active'" json:"status"`
+	Permissions string `gorm:"type:text" json:"permissions"`
+}