feat: single entry point routing — convert to front controller pattern

- Create app/public/index.php as front controller (bootstrap + Dispatcher)
- Rewrite app/router.php for PHP dev server → all non-asset requests to index.php
- Update Dispatcher to render full page layouts (head+header+view+footer)
- Move public view templates into templates/public/ (home, search, tfe, about, repertoire)
- Delete dead direct-access public/*.php files (apropos, search, tfe, licence, repertoire)
- Add clean URL routes to Dispatcher (/search, /tfe, /repertoire, /apropos, /licence, /media)
- Remove .php extensions from all internal links (header, views, templates, URLs)
- Update OG tags in controllers to use clean URLs
- Update nginx posterg.conf → front-controller try_files pattern, block direct .php access
- Update header.php and search-bar.php form actions to clean URLs
- Switch AboutController nav key from 'nav' to 'currentNav' for consistency

app/src/Controllers/AboutController.php

@@ -30,7 +30,7 @@ class AboutController {
         $pd->setSafeMode(true);
 
         return [
-            'nav'             => 'apropos',
+            'currentNav'      => 'apropos',
             'aboutHtml'       => $pd->text($rawContent),
             'contacts'        => $contacts,
             'credits'         => $credits,