refactor(handlers): replace temporary variable pointer pattern with new() builtin

Simplify pointer creation across kobo, koreader, and queue handlers by
replacing the two-step pattern (assign to local, then take address) with
inline new() calls. This reduces verbosity without changing behavior:

Before:
  remaining := int(a - b)
  pagesRemaining = &remaining

After:
  pagesRemaining = new(int(a - b))

Covers page calculations, chapter/progress fields, UUID formatting,
and timestamp string conversions.

internal/handlers/koreader.go

@@ -601,24 +601,19 @@ func (h *KOReaderHandler) GetMetadata(c *echo.Context) error {
 		progressData.Epubcfi = &progress.Epubcfi.String
 	}
 	if progress.Chapter.Valid {
-		ch := int(progress.Chapter.Int32)
-		progressData.Chapter = &ch
+		progressData.Chapter = new(int(progress.Chapter.Int32))
 	}
 	if progress.ChapterProgress.Valid {
-		cp := progress.ChapterProgress.Float64
-		progressData.ChapterProgress = &cp
+		progressData.ChapterProgress = new(progress.ChapterProgress.Float64)
 	}
 	if progress.CharacterOffset.Valid {
-		co := int64(progress.CharacterOffset.Int64)
-		progressData.Character = &co
+		progressData.Character = new(int64(progress.CharacterOffset.Int64))
 	}
 	if progress.CurrentPage.Valid {
-		cp := int(progress.CurrentPage.Int32)
-		progressData.Page = &cp
+		progressData.Page = new(int(progress.CurrentPage.Int32))
 	}
 	if progress.TotalPages.Valid {
-		tp := int(progress.TotalPages.Int32)
-		progressData.TotalPages = &tp
+		progressData.TotalPages = new(int(progress.TotalPages.Int32))
 	}
 
 	annotations, err := h.db.GetAnnotationsForBook(c.Request().Context(), database.GetAnnotationsForBookParams{
@@ -698,8 +693,7 @@ func (h *KOReaderHandler) GetLibrary(c *echo.Context) error {
 		if err == nil {
 			percentRead = progress.Percentage.Float64
 			if progress.TotalPages.Valid && progress.CurrentPage.Valid {
-				remaining := int(progress.TotalPages.Int32 - progress.CurrentPage.Int32)
-				pagesRemaining = &remaining
+				pagesRemaining = new(int(progress.TotalPages.Int32 - progress.CurrentPage.Int32))
 			}
 			if progress.LastReadAt.Valid {
 				lastModified = progress.LastReadAt.Time.Format(time.RFC3339)