feat: wire up Program.cs, DI extensions, Serilog, and appsettings

- ServiceCollectionExtensions in DAL.EF: AddNotificationDataAccess (DbContext, UoW, repositories)
- ServiceCollectionExtensions in Services: AddNotificationServices (MediatR + TransactionBehavior)
- Api/Program.cs: Serilog, OpenAPI, controllers, DI wiring
- Worker/Program.cs: Serilog, DI wiring
- appsettings.json: Serilog config with Console + Seq sinks, connection string
- appsettings.Development.json: Debug log level overrides

Ref: IT-628

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

HrynCo.NotificationService.Api/appsettings.json

@@ -1,9 +1,26 @@
 {
-  "Logging": {
-    "LogLevel": {
+  "ConnectionStrings": {
+    "Default": "Host=localhost;Port=5432;Database=notification_service;Username=postgres;Password=postgres"
+  },
+  "Serilog": {
+    "MinimumLevel": {
       "Default": "Information",
-      "Microsoft.AspNetCore": "Warning"
-    }
+      "Override": {
+        "Microsoft": "Warning",
+        "Microsoft.EntityFrameworkCore": "Warning",
+        "Microsoft.AspNetCore": "Warning"
+      }
+    },
+    "WriteTo": [
+      { "Name": "Console" },
+      {
+        "Name": "Seq",
+        "Args": {
+          "serverUrl": "http://localhost:5341"
+        }
+      }
+    ],
+    "Enrich": [ "FromLogContext" ]
   },
   "AllowedHosts": "*"
-}
+}