fix(database): correct mismatched parentheses in detect_fixed_layout_epub

The string_to_array call in detect_fixed_layout_epub() had an extra
closing parenthesis after the '<img' delimiter, causing a SQL syntax
error that prevented the database container from initializing:

  IF array_length(string_to_array(opf_content, '<img')), 1) - 1 > 50

Fixed to:

  IF array_length(string_to_array(opf_content, '<img'), 1) - 1 > 50

database/schema/schema.sql

@@ -755,7 +755,7 @@ BEGIN
   
   -- Check for image-heavy content (count <img> tags)
   -- Threshold of 50 images suggests manga/comic vs novel
-  IF array_length(string_to_array(opf_content, '<img')), 1) - 1 > 50 THEN
+  IF array_length(string_to_array(opf_content, '<img'), 1) - 1 > 50 THEN
     RETURN TRUE;
   END IF;