Phase 3: Code clean-up (v1.6.0)

[khoipro]

Phase 3 — Code Clean-up

Dead code removal

• Remove admin/partials/display.php — confirmed unused (admin rendered by Options Page class)
• Remove empty admin/js/codetot-optimization-admin.js — empty boilerplate
• Remove empty admin/css/codetot-optimization-admin.css — empty boilerplate

Security fixes

• Fix unescaped $GLOBALS[title] in admin options page (add esc_html())
• Add input sanitization for $_GET[gf_page] and $_POST[gform_ajax] in Gravity Forms class

Code quality

• Fix mixed indentation consistency in includes/ files