feat(backend): Wahl-Phasen, Verantwortliche-Invites, Auth fixes

- New VerantwortlicheInvite model: LT-issued invites so a person can
  register as Gemeinde Verantwortliche(r) for a specific Gemeinde,
  skipping the self-registration approval step.
- Wahl/Workshop/Teilnehmer gain phase support (phasenAnzahl,
  beschreibung), mirroring the WP plugin's multi-phase elections.
  Teilnehmer unique constraint now scoped per phase.
- Auth: team login + guest auth adjustments, spec coverage.
- sync.service.ts: register VerantwortlicheInvite as a synced model.
- wahl.service.ts: submitTeilnehmer updated for the new phase-scoped
  unique key.
- client: login/home screen rework, new theme.dart, FCM web tweaks.
- .gitignore: ignore .DS_Store.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

client/app/lib/screens/home_screen.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart';
 
 import '../api.dart';
 import '../main.dart';
+import '../theme.dart';
 import 'admin_screen.dart';
 import 'chat_screen.dart';
 import 'files_screen.dart';
@@ -109,8 +110,7 @@ class _IdentityCard extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final lines = <String>[
-      'Rolle: ${id.roleLabel}',
-      if (id.email != null) 'E-Mail: ${id.email}',
+      if (id.email != null) id.email!,
       if (id.isLeitungsteam)
         'Leitungsteam-Rechte gelten KC-übergreifend.'
       else if (id.memberships.length > 1)
@@ -118,13 +118,35 @@ class _IdentityCard extends StatelessWidget {
     ];
     return Card(
       child: Padding(
-        padding: const EdgeInsets.all(16),
-        child: Column(
-          crossAxisAlignment: CrossAxisAlignment.start,
+        padding: const EdgeInsets.all(20),
+        child: Row(
           children: [
-            Text('Angemeldet', style: Theme.of(context).textTheme.labelMedium),
-            const SizedBox(height: 4),
-            for (final l in lines) Text(l),
+            Container(
+              width: 48,
+              height: 48,
+              decoration: BoxDecoration(
+                gradient: const LinearGradient(
+                  colors: [KcColors.blue, KcColors.teal],
+                  begin: Alignment.topLeft,
+                  end: Alignment.bottomRight,
+                ),
+                shape: BoxShape.circle,
+              ),
+              child: const Icon(Icons.person, color: Colors.white),
+            ),
+            const SizedBox(width: 14),
+            Expanded(
+              child: Column(
+                crossAxisAlignment: CrossAxisAlignment.start,
+                children: [
+                  Text(id.roleLabel, style: Theme.of(context).textTheme.titleMedium),
+                  for (final l in lines) ...[
+                    const SizedBox(height: 2),
+                    Text(l, style: Theme.of(context).textTheme.bodySmall),
+                  ],
+                ],
+              ),
+            ),
           ],
         ),
       ),
@@ -147,12 +169,38 @@ class _NavTile extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return Card(
-      child: ListTile(
-        leading: Icon(icon),
-        title: Text(title),
-        subtitle: Text(subtitle),
-        trailing: const Icon(Icons.chevron_right),
+      margin: const EdgeInsets.only(bottom: 12),
+      child: InkWell(
+        borderRadius: BorderRadius.circular(20),
         onTap: onTap,
+        child: Padding(
+          padding: const EdgeInsets.all(16),
+          child: Row(
+            children: [
+              Container(
+                width: 44,
+                height: 44,
+                decoration: BoxDecoration(
+                  color: KcColors.blue.withValues(alpha: 0.1),
+                  borderRadius: BorderRadius.circular(12),
+                ),
+                child: Icon(icon, color: KcColors.blue),
+              ),
+              const SizedBox(width: 14),
+              Expanded(
+                child: Column(
+                  crossAxisAlignment: CrossAxisAlignment.start,
+                  children: [
+                    Text(title, style: Theme.of(context).textTheme.titleMedium),
+                    const SizedBox(height: 2),
+                    Text(subtitle, style: Theme.of(context).textTheme.bodySmall),
+                  ],
+                ),
+              ),
+              Icon(Icons.chevron_right, color: KcColors.slate.withValues(alpha: 0.6)),
+            ],
+          ),
+        ),
       ),
     );
   }