feat: add server logs functionality with role-based access and system channel management

- Introduced a new migration to add the IsSystem column to the Channels table.
- Updated the DbContext model snapshot to reflect the new IsSystem property.
- Enhanced the ChannelService to manage system channels, including creation, visibility control, and protection against deletion.
- Implemented ServerLogsService to handle live server logging, including reading from log files and managing access based on user roles.
- Created ServerLogsSink to queue log events for streaming to the live log room.
- Developed ServerLogsStreamService to stream log events to clients in real-time.
- Added configuration options for server logs in appsettings.
- Implemented comprehensive unit tests for channel service system channel behavior and server logs functionality.

src/EchoHub.Server/appsettings.example.json

@@ -47,6 +47,15 @@
     "Key": "",
     "EncryptDatabase": false
   },
+  "ServerLogs": {
+    "Enabled": true,
+    "RoomName": "server-logs",
+    "MinRole": "Mod",
+    "MinLevel": "Information",
+    "BacklogLines": 100,
+    "LogDirectory": "logs",
+    "LogFilePattern": "echohub-server-*.log"
+  },
   "Irc": {
     "Enabled": false,
     "Port": 6667,