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>

translations/messages.de.yaml

@@ -108,7 +108,7 @@ survey:
     answer_no: "Nein"
     answer_maybe: "Vielleicht"
     question_progress: "Frage %current%"
-    answer_flow_hint: "Diese Antwort wird direkt für den weiteren Ablauf verwendet."
+    jump_to: "weiter zu Frage %position%: %label%"
     current_value: "Aktueller Wert"
     back: "Zurück"
     next: "Weiter"

translations/messages.en.yaml

@@ -108,7 +108,7 @@ survey:
     answer_no: "No"
     answer_maybe: "Maybe"
     question_progress: "Question %current%"
-    answer_flow_hint: "This answer is used directly for the further flow."
+    jump_to: "continue to question %position%: %label%"
     current_value: "Current value"
     back: "Back"
     next: "Next"