fix: parse JSON error messages and redirect to dashboard

1. Parse JSON error responses to extract 'detail' field
   Fixes: {"detail":"..."} shown as raw JSON instead of clean text
2. Redirect 'already_verified' to '/' instead of '/login'
   Fixes: Users land on empty page when already logged in
3. Change button text: "Jetzt anmelden" → "Weiter zum Dashboard"

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/pages/Verify.jsx

@@ -42,15 +42,23 @@ export default function Verify() {
           setError('Verifizierung erfolgreich, aber Login fehlgeschlagen')
         }
       } catch (err) {
-        const errorMsg = err.message || 'Verifizierung fehlgeschlagen'
+        let errorMsg = err.message || 'Verifizierung fehlgeschlagen'
+
+        // Try to parse JSON error response
+        try {
+          const parsed = JSON.parse(errorMsg)
+          if (parsed.detail) errorMsg = parsed.detail
+        } catch (e) {
+          // Not JSON, use as-is
+        }
 
         // Check if already verified or already used
         if (errorMsg.includes('bereits bestätigt') || errorMsg.includes('already verified') ||
             errorMsg.includes('bereits verwendet') || errorMsg.includes('already used')) {
           setStatus('already_verified')
           setError(errorMsg) // Show the actual message
-          // Auto-redirect to login after 3 seconds
-          setTimeout(() => { window.location.href = '/login' }, 3000)
+          // Auto-redirect to dashboard after 3 seconds (let App.jsx decide login vs dashboard)
+          setTimeout(() => { window.location.href = '/' }, 3000)
         }
         // Check if token expired
         else if (errorMsg.includes('abgelaufen') || errorMsg.includes('expired')) {
@@ -218,10 +226,10 @@ export default function Verify() {
         </div>
 
         <button
-          onClick={() => navigate('/login')}
+          onClick={() => { window.location.href = '/' }}
           className="btn btn-primary btn-full"
         >
-          Jetzt anmelden
+          Weiter zum Dashboard
         </button>
       </div>
     )