feat: flashcards module - deck list, study mode, SM-2 review, session summary

edu/api/decks.php

@@ -0,0 +1,30 @@
+<?php
+$user_id = require_auth();
+
+// GET /api/decks
+if (get_method() === 'GET' && empty($segments[1])) {
+    $stmt = $pdo->prepare("
+        SELECT d.id, d.slug, d.name, d.description, d.card_count,
+            COUNT(cp.id) AS reviewed,
+            COUNT(cp.id) FILTER (WHERE cp.last_rating IN ('easy','medium')) AS correct,
+            COUNT(cp.id) FILTER (WHERE cp.next_review <= CURRENT_DATE) AS due
+        FROM decks d
+        LEFT JOIN cards c ON c.deck_id = d.id
+        LEFT JOIN card_progress cp ON cp.card_id = c.id AND cp.user_id = :uid
+        GROUP BY d.id
+        ORDER BY d.sort_order, d.name
+    ");
+    $stmt->execute([':uid' => $user_id]);
+    json_ok(['decks' => $stmt->fetchAll()]);
+}
+
+// GET /api/decks/{slug}
+if (get_method() === 'GET' && !empty($segments[1])) {
+    $stmt = $pdo->prepare("SELECT * FROM decks WHERE slug = :s");
+    $stmt->execute([':s' => $segments[1]]);
+    $deck = $stmt->fetch();
+    if (!$deck) json_error('Deck nicht gefunden', 404);
+    json_ok(['deck' => $deck]);
+}
+
+json_error('Methode nicht erlaubt', 405);