feat: add periodic server stats reporting and logging

- Introduced ServerStatsReport and ServerStatsCollector for tracking server activity.
- Implemented ServerStatsReportService to generate and persist stats reports periodically.
- Added configuration options for stats reporting in appsettings and .env.example.
- Enhanced logging in ChannelsController and ModerationController to include stats-related actions.
- Updated database context and migrations to support new ServerStatsReport entity.
- Adjusted logging levels in IrcGatewayService and ChatService for better performance.

src/EchoHub.Server/appsettings.example.json

@@ -56,6 +56,11 @@
     "LogDirectory": "logs",
     "LogFilePattern": "echohub-server-*.log"
   },
+  "Stats": {
+    "Enabled": true,
+    "IntervalHours": 6,
+    "RetentionDays": 90
+  },
   "Irc": {
     "Enabled": false,
     "Port": 6667,