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>

public/js/survey-backend.js

@@ -108,9 +108,29 @@
     document.addEventListener('DOMContentLoaded', normalizeSearchField);
     document.addEventListener('turbo:load', normalizeSearchField);
 
-    var observer = new MutationObserver(function () {
-        normalizeSearchField();
-    });
+    // Mutationen werden gebündelt: viele DOM-Änderungen lösen nur einen
+    // normalizeSearchField-Lauf pro Frame aus statt einen pro Mutation.
+    var scheduled = false;
+    var scheduleNormalize = function () {
+        if (scheduled) {
+            return;
+        }
+
+        scheduled = true;
+
+        var run = function () {
+            scheduled = false;
+            normalizeSearchField();
+        };
+
+        if (typeof window.requestAnimationFrame === 'function') {
+            window.requestAnimationFrame(run);
+        } else {
+            window.setTimeout(run, 100);
+        }
+    };
+
+    var observer = new MutationObserver(scheduleNormalize);
 
     observer.observe(document.documentElement, { childList: true, subtree: true });
 })();