* fix: correct case-sensitive require_once paths and add AGENTS.md for AI guidance
- Fix includes/plugin.php -> includes/Plugin.php in main plugin file
- Fix includes/core.php -> includes/Core.php in includes/Plugin.php
(Linux case-sensitive filesystems fail silently on macOS; runtime bug on production)
- Fix .ai-workflows/folder-structure.md: update class files to PascalCase,
remove references to non-existent admin/ subdirectories (images/, partials/,
settings/, tools/) that caused read:file_not_found errors in AI sessions
- Add AGENTS.md with authoritative file map to reduce AI agent errors:
edit:not_read_first, bash:other, edit:edit_stale_read, read:file_not_found
Resolves#13
* fix: markdown formatting in AGENTS.md (Codacy MD022/MD032)
