feat: add Migrator console project

- Dedicated HrynCo.NotificationService.Migrator console app
- Reads App:ConnectionString from config/env
- Calls db.Database.MigrateAsync() with clear log output
- Own Dockerfile (runtime:10.0 base, no SDK overhead)
- Replaces SDK volume-mount approach in docker-compose
- Added to solution with /docker/Migrator/ folder

Ref: IT-628

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

docker/environments/docker-compose.yml

@@ -1,18 +1,13 @@
 services:
   migrator:
-    image: mcr.microsoft.com/dotnet/sdk:10.0
-    working_dir: /src
-    volumes:
-      - ../..:/src
+    build:
+      context: ../..
+      dockerfile: HrynCo.NotificationService.Migrator/Dockerfile
     environment:
       - App__ConnectionString=${CONNECTION_STRING}
     depends_on:
       db:
         condition: service_started
-    command:
-      - /bin/sh
-      - -c
-      - dotnet tool install --tool-path /tmp/dotnet-tools dotnet-ef --version "9.*" && until /tmp/dotnet-tools/dotnet-ef database update --project /src/HrynCo.NotificationService.DAL.EF --startup-project /src/HrynCo.NotificationService.Web; do echo "Migration failed, retrying in 3s..."; sleep 3; done
     restart: "no"
 
   api: