feat: introduce AppSettings per application

- AppSettings class in Api and Worker with SectionName constant
- appsettings.json: replaced ConnectionStrings section with App section
- Program.cs: bind AppSettings at startup, register as singleton
- Connection string now sourced from AppSettings.ConnectionString

Ref: IT-628

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

HrynCo.NotificationService.Worker/AppSettings.cs

@@ -0,0 +1,8 @@
+namespace HrynCo.NotificationService.Worker;
+
+public sealed class AppSettings
+{
+    public const string SectionName = "App";
+
+    public string ConnectionString { get; init; } = string.Empty;
+}

HrynCo.NotificationService.Worker/Program.cs

@@ -8,10 +8,12 @@ var builder = Host.CreateApplicationBuilder(args);
 builder.Services.AddSerilog(lc =>
     lc.ReadFrom.Configuration(builder.Configuration));
 
-string connectionString = builder.Configuration.GetConnectionString("Default")
-    ?? throw new InvalidOperationException("Connection string 'Default' is not configured.");
+var appSettings = builder.Configuration
+    .GetSection(AppSettings.SectionName)
+    .Get<AppSettings>() ?? throw new InvalidOperationException("App settings are not configured.");
 
-builder.Services.AddNotificationDataAccess(connectionString);
+builder.Services.AddSingleton(appSettings);
+builder.Services.AddNotificationDataAccess(appSettings.ConnectionString);
 builder.Services.AddNotificationServices();
 builder.Services.AddHostedService<Worker>();
 

HrynCo.NotificationService.Worker/appsettings.json

@@ -1,6 +1,6 @@
 {
-  "ConnectionStrings": {
-    "Default": "Host=localhost;Port=5432;Database=notification_service;Username=postgres;Password=postgres"
+  "App": {
+    "ConnectionString": "Host=localhost;Port=5432;Database=notification_service;Username=postgres;Password=postgres"
   },
   "Serilog": {
     "MinimumLevel": {