fix: resolve recurring iOS PWA forbidden errors via CSRF response header

iOS Safari in PWA standalone mode unreliably handles cookies, causing
CSRF token desync between client and server after app resume. Previous
fixes (response body token in /auth/me and /auth/login) still left a
window where the token could go stale.

Now the server sends X-CSRF-Token response header on every API response
(via csrfMiddleware), including 403 error responses. The client reads
this header from every response, enabling instant self-healing: a 403
extracts the correct token from the error response itself and retries
without needing an extra /auth/me round-trip.

SW cache bumped to v33 to ensure existing iOS PWA installs pick up the
new client code.

public/api.js

@@ -52,6 +52,14 @@ async function apiFetch(path, options = {}, _retried = false) {
   // CSRF-Token-Desync (haeufig nach iOS-PWA-Resume): einmal GET /auth/me
   // ausfuehren um den CSRF-Token zu erneuern, dann den Request wiederholen.
   if (response.status === 403 && stateChanging && !_retried) {
+    // Token aus der 403-Antwort selbst extrahieren (Server liefert den
+    // korrekten Token im Header mit, auch bei Fehlschlag)
+    const errorCsrf = response.headers.get('X-CSRF-Token');
+    if (errorCsrf) {
+      _csrfToken = errorCsrf;
+      return apiFetch(path, options, true);
+    }
+    // Fallback: /auth/me aufrufen um Token zu erneuern
     const meRes = await fetch(`${API_BASE}/auth/me`, { credentials: 'same-origin', cache: 'no-store' });
     if (meRes.status === 401) {
       window.dispatchEvent(new CustomEvent('auth:expired'));
@@ -62,9 +70,13 @@ async function apiFetch(path, options = {}, _retried = false) {
     return apiFetch(path, options, true);
   }
 
+  // CSRF-Token aus Response-Header extrahieren (wird bei jeder API-Antwort mitgeliefert)
+  const csrfHeader = response.headers.get('X-CSRF-Token');
+  if (csrfHeader) _csrfToken = csrfHeader;
+
   const data = await response.json().catch(() => null);
 
-  // CSRF-Token aus Response-Body extrahieren (zuverlaessiger als Cookie auf iOS)
+  // Fallback: CSRF-Token aus Response-Body (fuer /auth/me und /auth/login)
   if (data?.csrfToken) _csrfToken = data.csrfToken;
 
   if (!response.ok) {