feat: implement dashboard with authentication and event logging

- Added dashboard functionality at /status with Basic Auth using DASHBOARD_PASSWORD.
- Created server-side event logging to track catalog and university status.
- Implemented traffic metrics tracking and display on the dashboard.
- Enhanced API tests to cover new dashboard features and authentication.
- Introduced CSS and JS for dashboard styling and functionality.
- Added tests for dashboard access control and data retrieval.

server/diagnostics.js

@@ -31,7 +31,8 @@ export function diagnose(schedule) {
       code,
       message: message[code],
       ...(lesson && {
-        groups: lesson.groups,
+        // Word repeats a group in some headers ("24-ИЯ (РА)и-1_…и-2"): once is enough.
+        groups: [...new Set(lesson.groups)],
         day: lesson.day,
         start: lesson.start || null,
         raw: lesson.raw,