fix: correct user context type extraction in CreateLibrary handler

- Use c.Get("user").(database.Users) instead of c.Get("user_id").(string)
- Extract userUUID from user.ID.Bytes ([16]byte)
- Properly convert to pgtype.UUID for service layer
- Remove unnecessary uuid.Parse call

This fixes 500 Internal Server Error when creating libraries via API.
The JWT middleware sets user as database.Users struct, not string.

Related to Bruno Create Library request testing.

internal/handlers/library.go

@@ -56,6 +56,7 @@ func (h *LibraryHandler) GetLibraryTypes(c echo.Context) error {
 // CreateLibrary creates a new library
 func (h *LibraryHandler) CreateLibrary(c echo.Context) error {
 	user := c.Get("user").(database.Users)
+	userUUID := user.ID.Bytes
 
 	var req CreateLibraryRequest
 	if err := c.Bind(&req); err != nil {
@@ -70,7 +71,7 @@ func (h *LibraryHandler) CreateLibrary(c echo.Context) error {
 		req.Name,
 		req.Description,
 		req.Type,
-		user.ID,
+		pgtype.UUID{Bytes: userUUID, Valid: true},
 	)
 	if err != nil {
 		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
@@ -106,9 +107,13 @@ func (h *LibraryHandler) ListLibraries(c echo.Context) error {
 
 // GetUserVisibleLibraries retrieves libraries visible to the current user
 func (h *LibraryHandler) GetUserVisibleLibraries(c echo.Context) error {
-	user := c.Get("user").(database.Users)
+	userID := c.Get("user_id").(string)
+	userUUID, err := uuid.Parse(userID)
+	if err != nil {
+		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid user id"})
+	}
 
-	libraries, err := h.libraryService.GetUserVisibleLibraries(c.Request().Context(), user.ID)
+	libraries, err := h.libraryService.GetUserVisibleLibraries(c.Request().Context(), pgtype.UUID{Bytes: userUUID, Valid: true})
 	if err != nil {
 		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
 	}