Add admin-configurable device cap per user

- Add max_devices column to users table (default: 10)
- Add UpdateUserMaxDevices database query
- Add CountUserDevices database query
- Add UpdateUserMaxDevices handler with validation (1-100 devices)
- Add PUT /api/auth/users/:id/max-devices endpoint (admin only)
- Update UserList struct to include max_devices field
- Validate user ID format and max_devices range
- Return appropriate errors for invalid requests

internal/handlers/auth.go

@@ -473,15 +473,16 @@ func (h *AuthHandler) ListUsers(c echo.Context) error {
 	}
 
 	type UserList struct {
-		ID        string `json:"id"`
-		Email     string `json:"email"`
-		Username  string `json:"username"`
-		FirstName string `json:"first_name"`
-		LastName  string `json:"last_name"`
-		Theme     string `json:"theme"`
-		Role      string `json:"role"`
-		CreatedAt string `json:"created_at"`
-		UpdatedAt string `json:"updated_at"`
+		ID         string `json:"id"`
+		Email      string `json:"email"`
+		Username   string `json:"username"`
+		FirstName  string `json:"first_name"`
+		LastName   string `json:"last_name"`
+		Theme      string `json:"theme"`
+		Role       string `json:"role"`
+		MaxDevices int32  `json:"max_devices"`
+		CreatedAt  string `json:"created_at"`
+		UpdatedAt  string `json:"updated_at"`
 	}
 
 	var userList []UserList
@@ -855,6 +856,42 @@ func (h *AuthHandler) GetScanSettings(c echo.Context) error {
 	})
 }
 
+type UpdateUserMaxDevicesRequest struct {
+	MaxDevices int32 `json:"max_devices" validate:"required,min=1,max=100"`
+}
+
+// UpdateUserMaxDevices handles PUT /api/auth/users/:id/max-devices (admin only)
+func (h *AuthHandler) UpdateUserMaxDevices(c echo.Context) error {
+	userID := c.Param("id")
+	if userID == "" {
+		return c.JSON(http.StatusBadRequest, map[string]string{"error": "user id required"})
+	}
+
+	var req UpdateUserMaxDevicesRequest
+	if err := c.Bind(&req); err != nil {
+		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid request"})
+	}
+
+	if err := c.Validate(&req); err != nil {
+		return c.JSON(http.StatusBadRequest, map[string]string{"error": err.Error()})
+	}
+
+	userUUID, err := uuid.Parse(userID)
+	if err != nil {
+		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid user id"})
+	}
+
+	err = h.db.UpdateUserMaxDevices(c.Request().Context(), database.UpdateUserMaxDevicesParams{
+		ID:         pgtype.UUID{Bytes: userUUID, Valid: true},
+		MaxDevices: pgtype.Int4{Int32: req.MaxDevices, Valid: true},
+	})
+	if err != nil {
+		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
+	}
+
+	return c.JSON(http.StatusOK, map[string]string{"message": "max devices updated"})
+}
+
 // AdminMiddleware checks if the user has admin role
 func AdminMiddleware(next echo.HandlerFunc) echo.HandlerFunc {
 	return func(c echo.Context) error {