Template Error in projects.index: App\Models\Project::customer(): Return value must be of type Illuminate\Database\Eloquent\Relations\BelongsTo, App\Models\Customer returned

<!DOCTYPE html>
<html lang="de">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title><?= htmlspecialchars((string)(config('app.name', 'iasPen')), ENT_QUOTES, "UTF-8") ?> 1.0 — Architecture & Construction Platform</title>
  <link rel="stylesheet" href="/assets/css/app.css">
  <link rel="stylesheet" href="<?= htmlspecialchars((string)(asset('assets/css/app.css')), ENT_QUOTES, "UTF-8") ?>">
  <link rel="stylesheet" href="<?= htmlspecialchars((string)(asset('build/assets/app.css')), ENT_QUOTES, "UTF-8") ?>">
  <style>
    .active-nav { background-color: #1A1A1C !important; color: #FFFFFF !important; border-left-color: #E30613 !important; font-weight: 700 !important; }
  </style>
</head>
<body>
  <div class="app-container">
    
    <!-- SIDEBAR -->
    <aside class="sidebar">
      <div class="brand-header">
        <a href="<?= htmlspecialchars((string)(route('projects.index')), ENT_QUOTES, "UTF-8") ?>" class="brand-logo">
          <div class="brand-symbol">i</div>
          <span class="brand-title">iasPen</span>
        </a>
        <span class="brand-badge">Laravel 11</span>
      </div>

      <nav class="sidebar-nav">
        <div class="nav-section-title">Hauptmodule</div>
        
        <a href="<?= htmlspecialchars((string)(route('projects.index')), ENT_QUOTES, "UTF-8") ?>" class="nav-item <?= htmlspecialchars((string)(request()->routeIs('projects.*') ? 'active-nav' : ''), ENT_QUOTES, "UTF-8") ?>">
          <span>🏗</span>
          <span>Projekte & Workspace</span>
        </a>

        <a href="<?= htmlspecialchars((string)(route('customers.index')), ENT_QUOTES, "UTF-8") ?>" class="nav-item <?= htmlspecialchars((string)(request()->routeIs('customers.*') ? 'active-nav' : ''), ENT_QUOTES, "UTF-8") ?>">
          <span>👥</span>
          <span>Kundenstamm (CRM)</span>
        </a>

        <a href="<?= htmlspecialchars((string)(route('invoices.index')), ENT_QUOTES, "UTF-8") ?>" class="nav-item <?= htmlspecialchars((string)(request()->routeIs('invoices.*') ? 'active-nav' : ''), ENT_QUOTES, "UTF-8") ?>">
          <span>📑</span>
          <span>Angebote & Rechnungen</span>
        </a>

        <a href="<?= htmlspecialchars((string)(route('timesheets.index')), ENT_QUOTES, "UTF-8") ?>" class="nav-item <?= htmlspecialchars((string)(request()->routeIs('timesheets.*') ? 'active-nav' : ''), ENT_QUOTES, "UTF-8") ?>">
          <span>⏱</span>
          <span>Zeiterfassung</span>
        </a>

        <a href="<?= htmlspecialchars((string)(route('activity.index')), ENT_QUOTES, "UTF-8") ?>" class="nav-item <?= htmlspecialchars((string)(request()->routeIs('activity.*') ? 'active-nav' : ''), ENT_QUOTES, "UTF-8") ?>">
          <span>🕒</span>
          <span>Aktivitätsprotokoll</span>
        </a>

        <a href="<?= htmlspecialchars((string)(route('settings.index')), ENT_QUOTES, "UTF-8") ?>" class="nav-item <?= htmlspecialchars((string)(request()->routeIs('settings.*') ? 'active-nav' : ''), ENT_QUOTES, "UTF-8") ?>">
          <span>⚙</span>
          <span>Einstellungen</span>
        </a>

        <div style="margin-top: 24px; padding: 0 16px;">
          <a href="<?= htmlspecialchars((string)(route('projects.create')), ENT_QUOTES, "UTF-8") ?>" class="btn-swiss btn-swiss-red btn-swiss-sm" style="display: block; width: 100%; text-align: center;">
            + Neues Projekt
          </a>
        </div>
      </nav>

      <!-- Sidebar Footer -->
      <div class="sidebar-footer">
        <div class="user-role-card">
          <div class="user-avatar"><?= htmlspecialchars((string)(strtoupper(substr(auth()->user()->name ?? 'AD', 0, 2))), ENT_QUOTES, "UTF-8") ?></div>
          <div class="user-info" style="flex: 1;">
            <div class="user-name"><?= htmlspecialchars((string)(auth()->user()->name ?? 'Max Muster-Architekt'), ENT_QUOTES, "UTF-8") ?></div>
            <div style="font-size: 10px; color: #888; text-transform: capitalize;"><?= htmlspecialchars((string)(auth()->user()->role ?? 'Projektleiter'), ENT_QUOTES, "UTF-8") ?></div>
          </div>
          <a href="<?= htmlspecialchars((string)(route('logout')), ENT_QUOTES, "UTF-8") ?>" title="Abmelden" style="color: #E30613; text-decoration: none; font-size: 14px; font-weight: bold;">⏻</a>
        </div>
      </div>
    </aside>

    <!-- TOPBAR -->
    <header class="topbar">
      <div class="topbar-left">
        <a href="/public/install.php" class="doc-link">Webinstaller</a>
        <span class="breadcrumb-separator">/</span>
        <div class="breadcrumb">
          <span>iasPen Enterprise</span>
          
  <span class="breadcrumb-separator">/</span>
  <span>Projekte</span>

        </div>
      </div>
      
      <div class="topbar-right">
        <div class="server-status-pill">
          <span class="status-dot"></span>
          <span>ALL-INKL Production Mode</span>
        </div>
      </div>
    </header>

    <!-- MAIN VIEW CONTAINER -->
    <main class="main-content">
      <?php if(session('success')): ?>
        <div style="background: #196F3D; color: #fff; padding: 12px 16px; border-radius: 4px; font-size: 13px; margin-bottom: 20px; font-weight: 600;">
          ✓ <?= htmlspecialchars((string)(session('success')), ENT_QUOTES, "UTF-8") ?>
        </div>
      <?php endif; ?>

      <?php if($errors->any()): ?>
        <div style="background: #E30613; color: #fff; padding: 12px 16px; border-radius: 4px; font-size: 13px; margin-bottom: 20px;">
          <ul style="margin: 0; padding-left: 20px;">
            <?php foreach($errors->all() as $error): ?>
              <li><?= htmlspecialchars((string)($error), ENT_QUOTES, "UTF-8") ?></li>
            <?php endforeach; ?>
          </ul>
        </div>
      <?php endif; ?>

      
<div class="card-white">
  <div class="card-header-row">
    <div>
      <span class="card-title"><span class="sq-accent"></span>Bauprojekte & Mandate</span>
      <div style="font-size: 12px; color: #666;">Übersicht aller aktiven Bauvorhaben und Planungsphasen</div>
    </div>
    <a href="<?= htmlspecialchars((string)(route('projects.create')), ENT_QUOTES, "UTF-8") ?>" class="btn-swiss btn-swiss-red">+ Neues Projekt anlegen</a>
  </div>

  <div class="table-container">
    <table class="swiss-table">
      <thead>
        <tr>
          <th>Projektcode</th>
          <th>Projektname</th>
          <th>Auftraggeber</th>
          <th>Budget Netto</th>
          <th>Status</th>
          <th>Offene Aufgaben</th>
          <th>Aktion</th>
        </tr>
      </thead>
      <tbody>
        <?php foreach($projects as $p): ?>
          <tr>
            <td style="font-family: var(--font-mono); font-weight: 800;"><?= htmlspecialchars((string)($p->code), ENT_QUOTES, "UTF-8") ?></td>
            <td>
              <a href="<?= htmlspecialchars((string)(route('projects.show', $p->id)), ENT_QUOTES, "UTF-8") ?>" style="font-weight: 800; color: #111; text-decoration: none;">
                <?= htmlspecialchars((string)($p->name), ENT_QUOTES, "UTF-8") ?>
              </a>
              <div style="font-size: 11px; color: #777;"><?= htmlspecialchars((string)($p->city), ENT_QUOTES, "UTF-8") ?></div>
            </td>
            <td><?= htmlspecialchars((string)($p->customer->company_name ?? 'Kein Kunde'), ENT_QUOTES, "UTF-8") ?></td>
            <td>€ <?= htmlspecialchars((string)(number_format($p->budget, 2, ',', '.')), ENT_QUOTES, "UTF-8") ?></td>
            <td><span class="badge badge-approved"><?= htmlspecialchars((string)(strtoupper(str_replace('_', ' ', $p->status))), ENT_QUOTES, "UTF-8") ?></span></td>
            <td><?= htmlspecialchars((string)($p->open_tasks), ENT_QUOTES, "UTF-8") ?> / <?= htmlspecialchars((string)($p->total_tasks), ENT_QUOTES, "UTF-8") ?></td>
            <td>
              <a href="<?= htmlspecialchars((string)(route('projects.show', $p->id)), ENT_QUOTES, "UTF-8") ?>" class="btn-swiss btn-swiss-outline btn-swiss-sm">
                Workspace öffnen →
              </a>
            </td>
          </tr>
        <?php endforeach; ?>
      </tbody>
    </table>
  </div>
</div>

    </main>

  </div>
</body>
</html>