feat: consume transactional email notifications

Add contract validation, SMTP delivery results, terminal failure context, neutral development seeding, and local Docker setup.

Ref: IT-1033

docker/environments/install-development.cmd

@@ -0,0 +1,72 @@
+@echo off
+setlocal
+
+set "SCRIPT_DIR=%~dp0"
+for %%I in ("%SCRIPT_DIR%..\..") do set "REPOSITORY_ROOT=%%~fI"
+set "ENV_FILE=%SCRIPT_DIR%.env.Development"
+set "BASE_COMPOSE=%SCRIPT_DIR%docker-compose.yml"
+set "DEVELOPMENT_COMPOSE=%SCRIPT_DIR%docker-compose.Development.yml"
+
+where docker >nul 2>&1
+if errorlevel 1 goto docker_missing
+
+docker info >nul 2>&1
+if errorlevel 1 goto docker_unavailable
+
+if not exist "%ENV_FILE%" goto environment_missing
+
+pushd "%REPOSITORY_ROOT%"
+if errorlevel 1 goto repository_unavailable
+
+echo Validating the development Docker Compose configuration...
+docker compose --env-file "%ENV_FILE%" -f "%BASE_COMPOSE%" -f "%DEVELOPMENT_COMPOSE%" config --quiet
+if errorlevel 1 goto compose_invalid
+if /i "%~1"=="--validate-only" goto validation_complete
+
+echo Building and starting the Notification Service development environment...
+docker compose --env-file "%ENV_FILE%" -f "%BASE_COMPOSE%" -f "%DEVELOPMENT_COMPOSE%" up --build -d
+if errorlevel 1 goto installation_failed
+
+echo.
+docker compose --env-file "%ENV_FILE%" -f "%BASE_COMPOSE%" -f "%DEVELOPMENT_COMPOSE%" ps
+
+echo.
+echo Notification Service development environment is running.
+echo Admin:    http://localhost:5200/admin/channels
+echo RabbitMQ: http://localhost:15672
+echo Mailpit:  http://localhost:8025
+echo Seq:      http://localhost:5342
+echo.
+popd
+exit /b 0
+
+:validation_complete
+echo Development Docker Compose configuration is valid.
+popd
+exit /b 0
+
+:compose_invalid
+echo ERROR: The development Docker Compose configuration is invalid.
+popd
+exit /b 1
+
+:installation_failed
+echo ERROR: Failed to build or start the development environment.
+popd
+exit /b 1
+
+:docker_missing
+echo ERROR: Docker CLI was not found. Install and start Docker Desktop, then run this script again.
+exit /b 1
+
+:docker_unavailable
+echo ERROR: Docker is installed, but the Docker engine is not available. Start Docker Desktop and try again.
+exit /b 1
+
+:environment_missing
+echo ERROR: Development environment file was not found: "%ENV_FILE%"
+exit /b 1
+
+:repository_unavailable
+echo ERROR: Repository root is not available: "%REPOSITORY_ROOT%"
+exit /b 1