Implement fixed boilerplate structure for header and footer templates

[Blueibear]

CRITICAL FIXES:

1. FIXED HEADER TEMPLATE STRUCTURE

   • Replace LLM-generated header with fixed boilerplate
   • LLM only generates inner header content (logo, nav, etc.)
   • Fixed structure enforces DOCTYPE, html, head, body tags
   • Prevents malformed HTML generation
   • Remove all tags from header

2. FIXED FOOTER TEMPLATE STRUCTURE

   • Replace LLM-generated footer with fixed boilerplate
   • LLM only generates inner footer content (widgets, copyright)
   • Fixed structure enforces footer, wp_footer(), body, html closing tags
   • Remove all tags from footer
   • Prevent double-escaped quotes: date('Y') not date('Y')
   • Remove duplicate footer blocks

3. SANITIZATION AND VALIDATION

   • Add sanitize_php_code() function to remove escaping artifacts
   • Remove ' and " when outside actual PHP strings
   • Remove invisible unicode characters
   • Validate and strip accidentally generated structural tags

4. TEMPLATE ENFORCEMENT

   • Add is_stub_template() to detect placeholder/stub templates
   • Add ensure_full_template_structure() to enforce get_header(), , get_footer()
   • Add remove_duplicate_footers() to clean duplicate footer blocks
   • Always create content.php and content-none.php as safe defaults

5. PACKAGING FIXES

   • Exclude .git, .github, node_modules from ZIP archives
   • Exclude hidden files and directories
   • Exclude IDE files (.vscode, .idea) and cache files

This update prevents blank screens, malformed HTML, and PHP syntax errors by using fixed boilerplate structures that LLMs cannot break.