security: fix auth bypass, XSS, IDOR, command injection, session hardening, rate limiting

- Phase 1: Require authentication for API register endpoint; restrict role creation
- Phase 2: Add $fillable whitelist to Server model to prevent mass assignment
- Phase 3: Fix XSS via escapeHtml in sidebar, JSON_HEX_TAG in script embeds
- Phase 4: Add canView() checks to TerminalController history/clearHistory
- Phase 5: escapeshellarg() on certbot params, sanitize service names, regex-based command blocklist, suppress exception messages
- Phase 6: SESSION_SECURE=true, SameSite=Strict, logout via POST+CSRF, chmod 640 .env
- Phase 7: DB-based rate limiting replacing session-based, applied to API login/register

views/dashboard/index.php

@@ -165,7 +165,7 @@ $aggregatedMetrics = $aggregatedMetrics ?? [];
 
 <script src="https://cdn.jsdelivr.net/npm/chart.js@4.4.7/dist/chart.umd.min.js"></script>
 <script>
-const aggregatedData = <?= json_encode($aggregatedMetrics) ?>;
+const aggregatedData = <?= json_encode($aggregatedMetrics, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES) ?>;
 
 let aggregatedChart = null;