AdminPanel PHP Template

Overview
- Single entry point (`templ.php`) with SSR shell + AJAX fragment loading.
- Shared layout includes: `sidebar.php`, `header.php`, `footer.php`.
- Shared frontend runtime: `assets/app.js` and `assets/app.css`.

Implemented Pages
- `mainContent.php` (Dashboard)
- `content2.php` (Analytics)
- `online.php` (external AdminLTE link)

Routing
- Route allow-list is defined in `routes.php`.
- Add new page routes there instead of editing `templ.php` logic.

Runtime and Security Baseline
- `APP_DEBUG` controls debug visibility.
- `APP_LOG_FILE` controls server log destination (default: `logs/app.log`).
- Production-safe behavior hides internal errors from end users and logs details server-side.

Topbar and Navigation
- Sidebar mini mode and mobile open/close supported.
- Browser back/forward navigation supported via History API.
- Fullscreen icon now syncs on `fullscreenchange`.

Documentation and Standards
- Main docs are under `docs/`.
- Root policy docs: `CONTRIBUTING.md`, `SECURITY.md`.
- Browser review page: `docs.html`.
- Consolidated task list: `docs/TASKS.md`.