fix(myTischtennis): improve error detection during login process

- Introduced enhanced error detection for CAPTCHA and login failures by probing page text during cookie retrieval attempts.
- Reduced maximum polling attempts and adjusted polling interval for better performance and responsiveness.
- Updated error handling to provide clearer feedback on specific login issues encountered during the authentication process.

backend/clients/myTischtennisClient.js

@@ -547,7 +547,9 @@ class MyTischtennisClient {
 
       // Wait for auth cookie after submit (polling avoids timing races).
       let authCookieObj = null;
-      const maxAttempts = 80;
+      let detectedSubmitError = null;
+      const pollIntervalMs = 500;
+      const maxAttempts = 40; // ~20s max wait after submit
       for (let attempt = 0; attempt < maxAttempts; attempt++) {
         const cookies = await context.cookies();
         authCookieObj = cookies.find((c) => c.name === 'sb-10-auth-token')
@@ -557,7 +559,29 @@ class MyTischtennisClient {
           console.log('[myTischtennisClient.playwright] Auth cookie detected:', authCookieObj.name);
           break;
         }
-        await page.waitForTimeout(500);
+
+        // Probe page text periodically to fail fast instead of waiting full timeout.
+        if (attempt % 4 === 0) {
+          try {
+            const textContent = await page.locator('body').innerText({ timeout: 600 });
+            if (textContent?.includes('Captcha-Bestätigung fehlgeschlagen')) {
+              detectedSubmitError = 'Captcha-Bestätigung fehlgeschlagen';
+              break;
+            }
+            if (textContent?.includes('Captcha-Bestätigung ist erforderlich')) {
+              detectedSubmitError = 'Captcha-Bestätigung ist erforderlich';
+              break;
+            }
+            if (textContent?.includes('Ungültige E-Mail oder Passwort')) {
+              detectedSubmitError = 'Ungültige E-Mail oder Passwort';
+              break;
+            }
+          } catch (_readBodyErr) {
+            // ignore text read errors during polling
+          }
+        }
+
+        await page.waitForTimeout(pollIntervalMs);
       }
       if (!authCookieObj || !authCookieObj.value) {
         let errorText = null;
@@ -572,6 +596,9 @@ class MyTischtennisClient {
         } catch (_e) {
           // ignore text read errors
         }
+        if (!errorText && detectedSubmitError) {
+          errorText = detectedSubmitError;
+        }
         return {
           success: false,
           error: errorText