student_id-FK-Migration Stufe 1+2: Name-Joins -> student_sessions.student_id

- student_sessions: neue Spalte student_id (+Index), backfilled aus (class_id,display_name)
- Session::createStudent setzt student_id (per Lookup, falls nicht uebergeben)
- alle Joins students<->student_sessions von display_name auf student_id umgestellt:
  Benchmark.php, live.php (5x), results.php (4x + runs), modules.php, profile.php, progress.php (answers+runs)
- verlustfrei verifiziert (alt-Join == neu-Join, class 99/102)

Robuster gegen Umbenennung/Doppelnamen, indexierbare Joins.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

App/php/api/progress.php

@@ -44,7 +44,7 @@ if ($method === 'GET') {
 
     if ($studentId && $simId) {
         $progress = $db->fetchOne('SELECT level, xp, plays, best_stars FROM player_progress WHERE student_id = ? AND sim_id = ?', [$studentId, $simId]);
-        $answers = $db->fetchAll('SELECT phase, question_id, answer, correct, answered_at FROM assessment_answers WHERE session_id IN (SELECT id FROM student_sessions WHERE class_id = (SELECT class_id FROM students WHERE id = ?)) AND sim_id = ? ORDER BY answered_at DESC', [$studentId, $simId]);
+        $answers = $db->fetchAll('SELECT phase, question_id, answer, correct, answered_at FROM assessment_answers WHERE session_id IN (SELECT id FROM student_sessions WHERE student_id = ?) AND sim_id = ? ORDER BY answered_at DESC', [$studentId, $simId]);
         // Optional: alle Durchgänge mit results-JSON, wenn ?runs=1 → für Schüler-Eigen-Drilldown
         $runs = [];
         if (!empty($_GET['runs'])) {
@@ -59,7 +59,7 @@ if ($method === 'GET') {
                     "SELECT a.id, a.submitted_at, a.duration_ms, a.results
                        FROM assessments a
                        JOIN student_sessions ss ON ss.id = a.session_id
-                      WHERE ss.class_id = ? AND ss.display_name = ? AND a.sim_id = ?
+                      WHERE ss.student_id = ? AND a.sim_id = ?
                         AND a.results IS NOT NULL
                         AND (
                               JSON_EXTRACT(a.results, '$.stars')              IS NOT NULL
@@ -70,7 +70,7 @@ if ($method === 'GET') {
                         )
                       ORDER BY a.submitted_at DESC
                       LIMIT 50",
-                    [$student['class_id'], $student['display_name'], $simId]
+                    [$studentId, $simId]
                 );
                 foreach ($rows as $row) {
                     $row['results'] = $row['results'] ? json_decode($row['results'], true) : null;