v2.6.1 (Lyra): Welcome page, 404 handling, installatie docs, opschoning

Nieuwe features:
- Welkomstpagina bij lege content-map (nieuwe installatie detectie)
- 404-afhandeling binnen actieve theme via admin/static/404.html
- HTTP 404 status bij onbekende pagina's en missende taalprefix

Opschoning:
- Verwijderd: package.json, src/scss/, root .htaccess, themes/demo/
- Verwijderde vendor packages: php-mqtt/client, mustache/mustache
- AGENTS.md samengevoegd naar root, development/AGENTS.md verwijderd
- .gitignore opgeschoond (NPM/node_modules/.sass-cache verwijderd)

Documentatie:
- Installatie instructies toegevoegd aan README (Apache2/Nginx/PHP/composer)
- README en guide versie referenties bijgewerkt naar 2.6.1
- Release notes: docs/release-notes/v2.6.1.md

Tests:
- Pentest: 30/30 geslaagd, 0 vulnerabilities
- WCAG 2.1 AA: 25/25 geslaagd, 100% compliance
- Test scripts gebruiken Apache-URL i.p.v. localhost:8080

cms/core/class/CodePressCMS.php

@@ -449,10 +449,29 @@ class CodePressCMS {
         if (isset($_GET['guide']) || $pageCheck === 'guide') {
             return $this->getGuidePage();
         }
+
+        // Determine if the request has a valid language prefix
+        $availableLangs = array_keys($this->getAvailableLanguages());
+        $requestPath = parse_url($_SERVER['REQUEST_URI'] ?? '/', PHP_URL_PATH) ?? '/';
+        $requestPath = ltrim($requestPath, '/');
+        $langFromUrl = '';
+        if ($requestPath !== '' && in_array(explode('/', $requestPath)[0], $availableLangs, true)) {
+            $langFromUrl = explode('/', $requestPath)[0];
+        }
+
+        // No language prefix and not the root → 404
+        if ($langFromUrl === '' && $requestPath !== '' && $requestPath !== 'favicon.ico') {
+            return $this->getError404();
+        }
         
-        // Check if content directory is empty
+        // Check if content directory is empty — show welcome page for new installations
         if ($this->isContentDirEmpty()) {
-            return $this->getGuidePage();
+            $requestedPage = $_GET['page'] ?? '';
+            // Only show welcome page on the home URL; everything else is a 404
+            if (empty($requestedPage) || $requestedPage === $this->getEffectiveDefaultPage()) {
+                return $this->getWelcomePage();
+            }
+            return $this->getError404();
         }
         
         $page = $_GET['page'] ?? $this->getEffectiveDefaultPage();
@@ -1048,9 +1067,60 @@ class CodePressCMS {
         $files = scandir($contentDir);
         $files = array_diff($files, ['.', '..']);
         
+        // Filter out hidden files (e.g. .gitkeep) — only count visible content
+        $files = array_filter($files, function($f) {
+            return $f[0] !== '.';
+        });
+        
         return empty($files);
     }
     
+    /**
+     * Get welcome page content for new installations (empty content directory)
+     *
+     * Shows a clear "new installation" message with next steps when the
+     * content directory has no content files yet.
+     *
+     * @return array Welcome page data
+     */
+    private function getWelcomePage() {
+        $adminUrl = $this->buildAdminUrl();
+        $guideUrl = '/' . $this->currentLanguage . '/guide';
+
+        $content = '<div class="welcome-page">';
+        $content .= '<h1>' . htmlspecialchars($this->t('welcome_title')) . '</h1>';
+        $content .= '<p class="alert alert-info" role="alert">';
+        $content .= '<i class="bi bi-info-circle me-2" aria-hidden="true"></i>';
+        $content .= htmlspecialchars($this->t('welcome_intro'));
+        $content .= '</p>';
+
+        $content .= '<h2>' . htmlspecialchars($this->t('welcome_next_steps')) . '</h2>';
+        $content .= '<ol class="list-group list-group-numbered mb-4">';
+        $content .= '<li class="list-group-item">' . htmlspecialchars($this->t('welcome_step_1')) . '</li>';
+        $content .= '<li class="list-group-item">' . htmlspecialchars($this->t('welcome_step_2')) . '</li>';
+        $content .= '<li class="list-group-item">' . htmlspecialchars($this->t('welcome_step_3')) . '</li>';
+        $content .= '</ol>';
+
+        $content .= '<div class="d-flex flex-column flex-md-row gap-2 mb-4">';
+        $content .= '<a href="' . htmlspecialchars($adminUrl) . '" class="btn btn-primary">';
+        $content .= '<i class="bi bi-gear me-1" aria-hidden="true"></i> ';
+        $content .= htmlspecialchars($this->t('welcome_admin_link'));
+        $content .= '</a>';
+        $content .= '<a href="' . htmlspecialchars($guideUrl) . '" class="btn btn-outline-secondary">';
+        $content .= '<i class="bi bi-book me-1" aria-hidden="true"></i> ';
+        $content .= htmlspecialchars($this->t('welcome_guide_link'));
+        $content .= '</a>';
+        $content .= '</div>';
+        $content .= '</div>';
+
+        return [
+            'title' => $this->t('welcome_title'),
+            'content' => $content,
+            'layout' => 'full_content',
+            'metadata' => [],
+        ];
+    }
+
     /**
      * Get guide page content based on user language
      * 
@@ -1228,9 +1298,17 @@ class CodePressCMS {
      * @return array 404 page data
      */
     private function getError404() {
+        $staticFile = __DIR__ . '/../../../admin/static/404.html';
+        $body = file_exists($staticFile)
+            ? file_get_contents($staticFile)
+            : '<h1>404 - ' . $this->t('page_not_found') . '</h1><p>' . $this->t('page_not_found_text') . '</p>';
+
         return [
             'title' => $this->t('page_not_found'),
-            'content' => '<h1>404 - ' . $this->t('page_not_found') . '</h1><p>' . $this->t('page_not_found_text') . '</p>'
+            'content' => $body,
+            'layout' => 'full_content',
+            'metadata' => [],
+            'is_404' => true,
         ];
     }
     
@@ -1252,6 +1330,11 @@ class CodePressCMS {
         $page = $this->getPage();
         $this->pluginManager->doAction('onPageLoad', $page);
         $this->pluginManager->doAction('onBeforeRender');
+
+        // Set 404 status for not-found pages (rendered through the theme)
+        if (!empty($page['is_404'])) {
+            http_response_code(404);
+        }
         
         $menu = $this->getMenu();