feat: Add Create Channel dialog and related events

- Introduced CreateChannelDialog for user to create new channels with name and topic.
- Added OnCreateChannelRequested event in MainWindow for channel creation.
- Enhanced EchoHubConnection with OnReconnected event for connection state handling.
- Updated EchoHubDbContext to use application base directory for SQLite database path.
- Integrated Serilog for logging in EchoHub.Server.
- Refactored database initialization and migration logic into DatabaseSetup class.
- Implemented FirstRunSetup to ensure appsettings.json and generate JWT secret if needed.
- Updated appsettings files to configure Serilog logging.
- Enhanced error handling and logging in ChatHub methods for better traceability.

src/EchoHub.Server/Setup/FirstRunSetup.cs

@@ -0,0 +1,48 @@
+using System.Security.Cryptography;
+using System.Text.Json;
+using System.Text.Json.Nodes;
+
+namespace EchoHub.Server.Setup;
+
+public static class FirstRunSetup
+{
+    public static void EnsureAppSettings()
+    {
+        var contentRoot = Directory.GetCurrentDirectory();
+        var settingsPath = Path.Combine(contentRoot, "appsettings.json");
+        var examplePath = Path.Combine(contentRoot, "appsettings.example.json");
+
+        if (!File.Exists(settingsPath) && File.Exists(examplePath))
+        {
+            File.Copy(examplePath, settingsPath);
+            Console.WriteLine("Created appsettings.json from example config.");
+        }
+
+        if (!File.Exists(settingsPath))
+            return;
+
+        EnsureJwtSecret(settingsPath);
+    }
+
+    private static void EnsureJwtSecret(string settingsPath)
+    {
+        var json = File.ReadAllText(settingsPath);
+        var root = JsonNode.Parse(json, documentOptions: new JsonDocumentOptions { CommentHandling = JsonCommentHandling.Skip });
+        if (root is null)
+            return;
+
+        var currentSecret = root["Jwt"]?["Secret"]?.GetValue<string>();
+
+        if (!string.IsNullOrEmpty(currentSecret) && !currentSecret.StartsWith("CHANGE_ME"))
+            return;
+
+        var secret = Convert.ToBase64String(RandomNumberGenerator.GetBytes(48));
+
+        root["Jwt"] ??= new JsonObject();
+        root["Jwt"]!["Secret"] = secret;
+
+        var writeOptions = new JsonSerializerOptions { WriteIndented = true };
+        File.WriteAllText(settingsPath, root.ToJsonString(writeOptions));
+        Console.WriteLine("Generated new JWT secret in appsettings.json.");
+    }
+}