Add tenant dashboard (Phase 2)

Dashboard Features:
- Login page with session-based auth
- Overview page with live stats (viewers, stream status)
- Stream settings (URL, type configuration)
- Branding editor (colors, texts, custom CSS)
- Settings page (weather, content toggles, UI options)

New Files:
- dashboard/index.php: Main overview with stats
- dashboard/login.php: Authentication page
- dashboard/logout.php: Session cleanup
- dashboard/stream.php: Stream configuration
- dashboard/branding.php: Visual customization
- dashboard/settings.php: Feature toggles
- dashboard/templates/layout.php: Shared layout
- dashboard/api/stats.php: Stats API endpoint
- dashboard/assets/dashboard.css: Modern dashboard UI
- dashboard/assets/dashboard.js: Client-side functionality
- src/Auth/AuthManager.php: Secure auth with Argon2, remember-me

Auth Features:
- Secure password hashing (Argon2ID)
- Remember-me tokens
- Role-based access (super_admin, tenant_admin, tenant_user)
- Legacy fallback for existing admin credentials

aurora-livecam/dashboard/api/stats.php

@@ -0,0 +1,75 @@
+<?php
+/**
+ * Dashboard API - Stats
+ */
+
+header('Content-Type: application/json');
+
+require_once dirname(__DIR__, 2) . '/vendor/autoload.php';
+require_once dirname(__DIR__, 2) . '/SettingsManager.php';
+
+if (file_exists(dirname(__DIR__, 2) . '/src/bootstrap.php')) {
+    require_once dirname(__DIR__, 2) . '/src/bootstrap.php';
+}
+
+use AuroraLivecam\Auth\AuthManager;
+use AuroraLivecam\Core\Database;
+
+$auth = new AuthManager();
+
+// Auth check
+if (!$auth->isLoggedIn()) {
+    http_response_code(401);
+    echo json_encode(['success' => false, 'error' => 'Unauthorized']);
+    exit;
+}
+
+$user = $auth->getUser();
+$tenantId = $user['tenant_id'] ?? 0;
+
+$stats = [
+    'viewers_current' => 0,
+    'viewers_today' => 0,
+    'viewers_peak' => 0,
+    'stream_status' => 'unknown',
+];
+
+// Aktuelle Zuschauer aus Datei
+$viewerFile = dirname(__DIR__, 2) . '/active_viewers.json';
+if (file_exists($viewerFile)) {
+    $viewers = json_decode(file_get_contents($viewerFile), true);
+    $stats['viewers_current'] = count($viewers ?? []);
+}
+
+// DB Stats falls verfügbar
+try {
+    $db = Database::getInstance();
+
+    if ($tenantId > 0) {
+        $todayStats = $db->fetchOne(
+            "SELECT SUM(viewer_count) as total, MAX(viewer_count) as peak
+             FROM viewer_stats
+             WHERE tenant_id = ? AND DATE(recorded_at) = CURDATE()",
+            [$tenantId]
+        );
+
+        if ($todayStats) {
+            $stats['viewers_today'] = (int)($todayStats['total'] ?? 0);
+            $stats['viewers_peak'] = (int)($todayStats['peak'] ?? 0);
+        }
+
+        $stream = $db->fetchOne(
+            "SELECT last_status FROM tenant_streams WHERE tenant_id = ? AND is_primary = 1",
+            [$tenantId]
+        );
+        $stats['stream_status'] = $stream['last_status'] ?? 'unknown';
+    }
+} catch (\Exception $e) {
+    // DB nicht verfügbar - Stats bleiben auf Defaults
+}
+
+echo json_encode([
+    'success' => true,
+    'stats' => $stats,
+    'timestamp' => time(),
+]);