feat(clickTtPlayerRegistrationService): add debug HTML file generation for error diagnostics

- Introduced a new function to generate a timestamped HTML file containing the page content during error handling, improving diagnostics for failed registration attempts.
- Enhanced error reporting to include the path to the generated HTML file, providing better context for troubleshooting issues in the registration flow.

backend/services/clickTtPlayerRegistrationService.js

@@ -1,4 +1,5 @@
 import { chromium } from 'playwright';
+import { writeFile } from 'fs/promises';
 import Member from '../models/Member.js';
 import Club from '../models/Club.js';
 import ClickTtAccount from '../models/ClickTtAccount.js';
@@ -35,6 +36,11 @@ function escapeRegExp(value) {
   return String(value).replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
 }
 
+function buildDebugHtmlPath() {
+  const timestamp = new Date().toISOString().replace(/[:.]/g, '-');
+  return `/tmp/clicktt-debug-${timestamp}.html`;
+}
+
 class ClickTtPlayerRegistrationService {
   async submitExistingPlayerApplication({ userToken, userId, clubId, memberId }) {
     await checkAccess(userToken, clubId);
@@ -135,10 +141,17 @@ class ClickTtPlayerRegistrationService {
     } catch (error) {
       let diagnostics = {};
       try {
+        const html = await page?.content?.();
+        const htmlPath = html ? buildDebugHtmlPath() : null;
+        if (html && htmlPath) {
+          await writeFile(htmlPath, html, 'utf8');
+        }
+
         diagnostics = {
           url: page?.url?.() || null,
           text: sanitizePageText(await page?.locator?.('body')?.innerText?.()),
-          traceTail: trace.slice(-25)
+          traceTail: trace.slice(-25),
+          htmlPath
         };
       } catch (_err) {
         diagnostics = {};
@@ -146,13 +159,15 @@ class ClickTtPlayerRegistrationService {
 
       this._trace(trace, 'error', {
         message: error?.message || String(error),
-        url: diagnostics.url || null
+        url: diagnostics.url || null,
+        htmlPath: diagnostics.htmlPath || null
       });
       const message = error instanceof HttpError
         ? error.message
         : `Click-TT-Automatisierung fehlgeschlagen: ${error.message || error}`;
-      const wrappedError = new HttpError(`${message}${diagnostics.url ? ` (Seite: ${diagnostics.url})` : ''}${diagnostics.text ? ` - ${diagnostics.text}` : ''}`, error.statusCode || error.status || 500);
+      const wrappedError = new HttpError(`${message}${diagnostics.url ? ` (Seite: ${diagnostics.url})` : ''}${diagnostics.htmlPath ? ` (HTML: ${diagnostics.htmlPath})` : ''}${diagnostics.text ? ` - ${diagnostics.text}` : ''}`, error.statusCode || error.status || 500);
       wrappedError.trace = diagnostics.traceTail || [];
+      wrappedError.htmlPath = diagnostics.htmlPath || null;
       throw wrappedError;
     } finally {
       if (context) {