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/utils/mediaurl.go

@@ -33,3 +33,13 @@ func ResolveMediaURL(libraryID pgtype.UUID, relativePath pgtype.Text) string {
 	encodedPath := strings.Join(segments, "/")
 	return fmt.Sprintf("/uploads/library-%s/%s", libraryIDStr, encodedPath)
 }
+
+// PgTextString unwraps a nullable text column to a plain string (""
+// when NULL). The former textToString/getText/normText copies in
+// handlers, router, and utils all did exactly this.
+func PgTextString(t pgtype.Text) string {
+	if t.Valid {
+		return t.String
+	}
+	return ""
+}