feat(phase2): aircraft market, fleet management, finances, loans

- market.php: Buy new aircraft (6 types: Dash8 to A380)
- aircraft.php: Fleet management, crew assignment, route planning
- finances.php: Account balance, transactions, loans
- Database.php: Extended with loan/transaction/aircraft methods
- schema.sql: Aircraft types table, 10M starting balance, INSERT OR IGNORE
- dashboard.php: Updated with fleet/financial overview
- Fixed: duplicate function declarations in Database.php
- Fixed: initializeSchema() with idempotent error handling

www/public/dashboard.php

@@ -24,6 +24,10 @@ $todayStats = $db->getTodayStats($userId);
 $aircraft = $db->getUserAircraft($userId);
 $routes = $db->getUserRoutes($userId);
 
+// Kredite und Finanzen
+$totalDebt = $db->getTotalDebtWithInterest($userId);
+$maintenanceDue = $db->checkMaintenanceDue($userId);
+
 // Level-Fortschritt berechnen
 $expForNextLevel = $config['game']['level_up_threshold'] * pow($config['game']['level_multiplier'], $user['level'] - 1);
 $levelProgress = ($user['experience'] / $expForNextLevel) * 100;
@@ -47,9 +51,10 @@ $levelProgress = ($user['experience'] / $expForNextLevel) * 100;
             <button class="navbar-toggle" aria-label="Menü">☰</button>
             <ul class="navbar-menu">
                 <li><a href="<?= BASE_PATH ?>dashboard.php" class="navbar-item active">📊 Dashboard</a></li>
-                <li><a href="<?= BASE_PATH ?>airports.php" class="navbar-item">🌍 Weltkarte</a></li>
-                <li><a href="<?= BASE_PATH ?>airports.php?action=fleet" class="navbar-item">✈️ Flotte</a></li>
-                <li><a href="<?= BASE_PATH ?>airports.php?action=routes" class="navbar-item">🛫 Routen</a></li>
+                <li><a href="<?= BASE_PATH ?>airports.php" class="navbar-item">🌍 Flughäfen</a></li>
+                <li><a href="<?= BASE_PATH ?>aircraft.php" class="navbar-item">✈️ Flotte</a></li>
+                <li><a href="<?= BASE_PATH ?>finances.php" class="navbar-item">💰 Finanzen</a></li>
+                <li><a href="<?= BASE_PATH ?>market.php" class="navbar-item">🛒 Markt</a></li>
                 <li>
                     <span class="navbar-item">
                         💰 <?= formatMoney($user['balance']) ?>
@@ -124,6 +129,29 @@ $levelProgress = ($user['experience'] / $expForNextLevel) * 100;
                 <div class="stat-value"><?= formatNumber($stats['total_flights'] ?? 0) ?></div>
                 <div class="stat-label">Flüge (gesamt)</div>
             </div>
+            
+            <div class="stat-card">
+                <div class="stat-icon">🏦</div>
+                <div class="stat-value <?= $totalDebt > 0 ? 'text-warning' : '' ?>">
+                    <?= formatMoney($totalDebt) ?>
+                </div>
+                <div class="stat-label">Schulden</div>
+            </div>
+            
+            <div class="stat-card">
+                <div class="stat-icon">🔧</div>
+                <div class="stat-value <?= count($maintenanceDue) > 0 ? 'text-danger' : '' ?>">
+                    <?= count($maintenanceDue) ?>
+                </div>
+                <div class="stat-label">Wartung fällig</div>
+            </div>
+            
+            <?php if (!empty($maintenanceDue)): ?>
+            <div class="alert alert-warning mt-md mb-none">
+                ⚠️ Bei <?= count($maintenanceDue) ?> Flugzeug(en) ist die Wartung fällig!
+                <a href="<?= BASE_PATH ?>aircraft.php" class="btn btn-sm btn-warning ml-md">Jetzt warten</a>
+            </div>
+            <?php endif; ?>
         </div>
 
         <!-- Quick Actions -->