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/Config/StatsOptions.cs

@@ -0,0 +1,21 @@
+namespace EchoHub.Server.Config;
+
+/// <summary>
+/// Periodic server-stats report settings, bound from the "Stats" config section (env override:
+/// <c>Stats__Enabled</c> etc.). When enabled, a background job periodically snapshots server
+/// activity, logs it as pretty-printed JSON, and persists it to the database.
+/// </summary>
+public sealed class StatsOptions
+{
+    /// <summary>Master switch for the periodic stats report job.</summary>
+    public bool Enabled { get; set; } = true;
+
+    /// <summary>How often a report is generated, in hours. Default: every 6 hours.</summary>
+    public double IntervalHours { get; set; } = 6;
+
+    /// <summary>
+    /// How long persisted reports are kept before being pruned, in days. Set to 0 to keep
+    /// reports indefinitely. Default: 90 days.
+    /// </summary>
+    public int RetentionDays { get; set; } = 90;
+}