chore: #3628803 Fix coding standards, JavaScript lint errors and spelling

Fix existing PHP coding-standard violations, JavaScript lint errors and spelling findings. Add a project dictionary for valid terms while preserving caption and URL sanitization.

Validation:

• Drupal PHPCS, PHP syntax, ESLint and CSpell pass.
• Chromium comparisons confirm unchanged image and inline modal behavior, keyboard controls and sanitization.
• Compatible with pending MRs !14 (merged), !15 (merged), !16, !18 (merged) and !19 (merged).

Service-injection recommendations and remaining non-blocking JavaScript warnings are outside this MR.

Issue: https://www.drupal.org/project/glightbox/issues/3628803

AI-Generated: Yes (Codex prepared the changes and verification).