Fix frontend CSRF, clean reader URLs, and review findings

CSRF / actions:
- List action forms now send both REQUEST_TOKEN (Contao gate) and _token
  (Symfony, validated via isCsrfTokenValid) — mirrors the editor; fixes
  the 400/500 "Ungültiger CSRF-Token" on publish/toggle/duplicate/delete

Public reader / URLs:
- Reader & results read auto_item via Input::get (marks the route param used)
  so clean path URLs /<page>/<alias> no longer 404
- List controller generates path URLs via ['parameters' => '/'.$alias]
- Allow re-participation in the same session after a 60s cooldown

Review fixes:
- Results: merge answer snapshots by questionId+type (no more split cards on
  label edits); seed "Vielleicht" when allowMaybe so screen matches Excel
- Reader: replace generic answer hint with per-option "weiter zu Frage X"
  only when a jump is configured; strip HTML tags from survey description
- PDF: render free-text frequency summary; drop duplicate "Minimum" label
- Drag-sort: bundle SortableJS locally, drop the duplicated inline sort CSS/JS
  from _survey_assets, throttle the backend MutationObserver
- Backend: move hardcoded tl_survey operation labels to TL_LANG (de+en)
- Remove dead code: SurveyEditorVoter, SurveyPermissionService,
  categoryFilter/categorySummary + helpers, orphaned publishSurvey lang key

Reader layout:
- max-width 1000px (other views keep 1400px); back/next buttons fill the
  width as equal, card-sized halves; sort handle icon offset tweak

Docs: update AI_HANDOVER (dual-token CSRF, clean URLs) and README

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/Service/SurveyResultsPdfService.php

@@ -136,23 +136,19 @@ final class SurveyResultsPdfService
     private function buildChartLegend(array $questionResult): array
     {
         $chart = $questionResult['chart'] ?? null;
-
-        if (!is_array($chart)) {
-            return [];
-        }
-
-        $chartType = (string) ($chart['type'] ?? '');
+        $chartType = is_array($chart) ? (string) ($chart['type'] ?? '') : '';
         $sourceRows = match ($chartType) {
             'pie' => $questionResult['options'] ?? $questionResult['responseSummary'] ?? [],
             'line' => $questionResult['distribution'] ?? [],
-            default => [],
+            // Freitext hat kein Diagramm: Antwort-Häufigkeiten wie in der Online-Ansicht zeigen.
+            default => $questionResult['responseSummary'] ?? [],
         };
 
         if (!is_array($sourceRows) || [] === $sourceRows) {
             return [];
         }
 
-        $dataset = $chart['data']['datasets'][0] ?? [];
+        $dataset = is_array($chart) ? ($chart['data']['datasets'][0] ?? []) : [];
         $fillColors = match ($chartType) {
             'pie' => is_array($dataset['backgroundColor'] ?? null) ? $dataset['backgroundColor'] : [],
             'line' => is_array($dataset['pointBackgroundColor'] ?? null) ? $dataset['pointBackgroundColor'] : [],