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.

.env.example

@@ -75,3 +75,19 @@ Irc__Enabled=false
 
 # ── Logging ──────────────────────────────────────────────────────────
 # Serilog__MinimumLevel__Default=Information
+
+# ── Server logs room ─────────────────────────────────────────────────
+# Read-only system channel that live-streams Serilog events to Mod+ users.
+# ServerLogs__Enabled=true
+# ServerLogs__RoomName=server-logs
+# ServerLogs__MinRole=Mod
+# ServerLogs__MinLevel=Information
+# ServerLogs__BacklogLines=100
+# ServerLogs__LogDirectory=logs
+# ServerLogs__LogFilePattern=echohub-server-*.log
+
+# ── Periodic stats report ────────────────────────────────────────────
+# Aggregate activity snapshot logged as JSON and persisted to the DB.
+# Stats__Enabled=true
+# Stats__IntervalHours=6
+# Stats__RetentionDays=90