feat: licence page, admin pages editor, license types, gradient card placeholders, latest-year home view

- Feature 1: public /licence.php fetches 'licenses' page from DB, renders Markdown
- Feature 1: nav.php adds 'Licence' link with active state
- Feature 2: Database::getPage(), savePage(), getAllPages() methods
- Feature 2: bundled src/Parsedown.php (MIT, zero-dependency)
- Feature 2: apropos.php now renders 'about' page content from DB via Parsedown
- Feature 2: admin/pages.php (list) + admin/pages-edit.php (EasyMDE editor)
- Feature 2: admin/actions/page.php (auth+CSRF+validation+save)
- Feature 2: admin/head.php adds 'Pages statiques' nav link
- Feature 3: storage/schema.sql seeds 8 CC license types
- Feature 3: storage/migrations/003_seed_license_types.sql (applied to live DB)
- Feature 3: Database::getLicenseTypes() / getAllLicenseTypes()
- Feature 3: admin/add.php + formulaire.php: license_id field on add form
- Feature 3: admin/edit.php: license_id field on edit form with raw FK lookup
- Feature 3: tfe.php: shows 'Licence :' meta row when non-null
- Feature 6: main.css: .card__media--gradient styles
- Feature 6: index.php: deterministic HSL gradient placeholder cards
- Feature 6: Database::getLatestYearTheses() + getLatestPublishedYear()
- Feature 6: index.php default home = random latest-year theses with info label

public/admin/pages-edit.php

@@ -0,0 +1,67 @@
+<?php
+require_once __DIR__ . "/../../config/bootstrap.php";
+require_once __DIR__ . '/../../src/AdminAuth.php';
+AdminAuth::requireLogin();
+
+if (empty($_SESSION['csrf_token'])) {
+    $_SESSION['csrf_token'] = bin2hex(random_bytes(32));
+}
+
+require_once __DIR__ . '/../../src/Database.php';
+
+$allowedSlugs = ['about', 'licenses', 'charte', 'contact'];
+$slug = $_GET['slug'] ?? '';
+
+if (!in_array($slug, $allowedSlugs)) {
+    header('Location: /admin/pages.php');
+    exit;
+}
+
+try {
+    $db = new Database();
+    $page = $db->getPage($slug);
+    if (!$page) {
+        die("Page introuvable.");
+    }
+} catch (Exception $e) {
+    die("Erreur: " . htmlspecialchars($e->getMessage()));
+}
+
+$pageTitle = "Éditer : " . htmlspecialchars($page['title']);
+?>
+<?php require_once APP_ROOT . '/templates/admin/head.php'; ?>
+
+<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/easymde/dist/easymde.min.css">
+
+<main class="admin-main">
+    <h1 class="admin-page-title">Éditer : <?= htmlspecialchars($page['title']) ?></h1>
+
+    <form action="/admin/actions/page.php" method="post" class="admin-form">
+        <input type="hidden" name="csrf_token" value="<?= htmlspecialchars($_SESSION['csrf_token']) ?>">
+        <input type="hidden" name="slug" value="<?= htmlspecialchars($slug) ?>">
+
+        <div class="admin-form-row" style="align-items:start;">
+            <label class="admin-label" for="content">Contenu (Markdown) :</label>
+            <textarea class="admin-textarea" id="content" name="content"
+                      rows="20"><?= htmlspecialchars($page['content'] ?? '') ?></textarea>
+        </div>
+
+        <div class="admin-submit-wrap">
+            <button type="submit" class="admin-btn">Enregistrer</button>
+            <a href="/admin/pages.php" class="admin-btn-secondary" style="margin-left:.75rem;">Annuler</a>
+        </div>
+    </form>
+</main>
+
+<script src="https://cdn.jsdelivr.net/npm/easymde/dist/easymde.min.js"></script>
+<script>
+    var easyMDE = new EasyMDE({
+        element: document.getElementById('content'),
+        spellChecker: false,
+        status: ['lines', 'words'],
+        minHeight: '400px',
+        toolbarTips: true
+    });
+</script>
+
+<?php require_once APP_ROOT . '/templates/admin/footer.php'; ?>