refactor(utils): one PgTextString for the four pgtype.Text unwrappers

handlers textToString, router textToString, router getText, and utils
normText were four copies of the same NULL-to-empty unwrap (99 call
sites). One exported utils.PgTextString replaces them all; the private
normText (comparison normalizer) stays but is now the odd one out.

Harness fix found on the way: setupTestServer built a full wiring
literal for route registration and then RETURNED a second, sparser
literal that never copied AnnotationService — setup.AnnotationService
was always nil on the struct every test receives. Nobody noticed until
cross_library_move_test became the first caller (it previously used
the now-retired plain CreateMediaHighlight query); it now exercises
the real SaveHighlight path through the wired service.

internal/handlers/reader.go

@@ -3,6 +3,7 @@ package handlers
 import (
 	"bookhoard/internal/database"
 	"bookhoard/internal/services"
+	"bookhoard/internal/utils"
 	"context"
 	"errors"
 	"fmt"
@@ -124,10 +125,10 @@ func (h *ReaderHandler) ShowReader(c *echo.Context) error {
 	return c.JSON(http.StatusOK, map[string]interface{}{
 		"media_item_id":          mediaItemID,
 		"title":                  mediaItem.Title,
-		"author":                 textToString(mediaItem.Author),
-		"cover_image_path":       textToString(mediaItem.CoverImagePath),
+		"author":                 utils.PgTextString(mediaItem.Author),
+		"cover_image_path":       utils.PgTextString(mediaItem.CoverImagePath),
 		"library_type":           mediaItem.FormatGroup,
-		"mime_type":              textToString(mediaItem.MimeType),
+		"mime_type":              utils.PgTextString(mediaItem.MimeType),
 		"file_path":              mediaItem.FilePath,
 		"total_pages":            mediaItem.PageCount,
 		"chapter_count":          mediaItem.ChapterCount,