Add admin health page and printable 24h export

- add a protected health.php page for config, XMLTV and M3U diagnostics
- add shared admin/config helpers for authenticated internal tools
- add a styled 24h export page designed for PDF/print output
- add browser-side PNG export for the daily schedule
- update README with the new admin tools

README.md

@@ -43,6 +43,8 @@ This demo runs with sample XMLTV feeds to showcase the interface.
 - ⭐ **Favorites** — pin channels to the top of the grid, persisted in localStorage
 - 🌍 **i18n** — auto-detects browser language, supports EN / FR / ES (add your own in `locales/`)
 - ⚙️ **Re-editable setup** — protected by an admin key, no SSH required to update config
+- 🩺 **Admin health page** — check config, XMLTV, M3U, response times, and metadata coverage
+- 🖨️ **24h printable export** — generate a polished daily schedule for PDF/print and PNG export
 - 🔔 **Update notifications** — a badge appears in the topbar when a new release is available on GitHub
 - 🔄 **Auto-reload** EPG every 30 minutes
 - 0️⃣ **Zero build tooling** — vanilla PHP/JS/CSS, with bundled local assets
@@ -225,6 +227,13 @@ GridTV detects the missing config and automatically redirects you to the setup p
 
 Once submitted, `config.json` is created on the server. **The setup page becomes inaccessible until you re-enter your admin key.**
 
+Admin tools are available here once unlocked with the same key:
+
+```text
+http://guide.your-domain.com/health.php
+http://guide.your-domain.com/export.php
+```
+
 ---
 
 <details>
@@ -280,9 +289,10 @@ nano /var/www/gridtv/config.json
 gridtv/
 ├── index.php            # Entry point
 ├── setup.php            # Setup + re-configuration (admin key protected)
+├── health.php           # Admin diagnostics page
+├── export.php           # 24h printable export (PDF/image friendly)
 ├── proxy.php            # HTTP→HTTPS stream proxy
 ├── version.json         # Current version (used for update check)
-├── config.example.json  # Config template
 ├── Dockerfile
 ├── docker-compose.yml
 ├── .gitignore           # config.json excluded
@@ -485,9 +495,9 @@ GNU Affero General Public License v3.0 (AGPLv3)
 - **i18n** — EN / FR / ES with browser auto-detection, extensible via locales/
 - **Favorites** — pin channels to the top of the grid (localStorage)
 - **Setup re-editable** — protected by an admin key, auto-generated on first setup
+- **Admin health page** — diagnostics for config, XMLTV, M3U, timing, and metadata coverage
 - **Update notifications** — topbar badge links to latest GitHub release
 
 ### 🔜 Coming soon
 - **Dark/Light auto mode** — follow system preference when using the default theme
-- **Grid export** — export today's schedule as PDF or image
 </details>