Parameterize docker-compose for server deployment

Compose settings:

- Reworked docker-compose.yml to use environment-variable driven configuration.

- Added shared app env anchors for backend and worker to reduce duplication.

- Made ports, credentials, security limits, SMTP, and storage options configurable.

Production profile:

- Added docker-compose.prod.yml override to close internal service ports.

- Keeps external attack surface minimal for Linux server deployments.

Docs and ops:

- Added .env.docker.example with full variable set for server setup.

- Updated README with quick-start and production launch commands.

.env.docker.example

@@ -0,0 +1,57 @@
+# Core
+APP_NAME=BenyaMessenger
+ENVIRONMENT=production
+DEBUG=false
+API_V1_PREFIX=/api/v1
+AUTO_CREATE_TABLES=true
+SECRET_KEY=replace-with-long-random-secret
+JWT_ALGORITHM=HS256
+ACCESS_TOKEN_EXPIRE_MINUTES=30
+REFRESH_TOKEN_EXPIRE_DAYS=30
+EMAIL_VERIFICATION_TOKEN_EXPIRE_HOURS=24
+PASSWORD_RESET_TOKEN_EXPIRE_HOURS=1
+
+# DB
+POSTGRES_DB=messenger
+POSTGRES_USER=postgres
+POSTGRES_PASSWORD=postgres
+POSTGRES_PORT=5432
+
+# Redis
+REDIS_PORT=6379
+
+# MinIO
+MINIO_ROOT_USER=minioadmin
+MINIO_ROOT_PASSWORD=minioadmin
+MINIO_API_PORT=9000
+MINIO_CONSOLE_PORT=9001
+S3_REGION=us-east-1
+S3_BUCKET_NAME=messenger-media
+S3_PRESIGN_EXPIRE_SECONDS=900
+MAX_UPLOAD_SIZE_BYTES=104857600
+
+# Public URLs
+FRONTEND_BASE_URL=http://localhost
+WEB_PORT=80
+BACKEND_PORT=8000
+
+# Mail
+SMTP_HOST=mailpit
+SMTP_PORT=1025
+SMTP_USERNAME=
+SMTP_PASSWORD=
+SMTP_USE_TLS=false
+SMTP_FROM_EMAIL=no-reply@benyamessenger.local
+MAILPIT_SMTP_PORT=1025
+MAILPIT_UI_PORT=8025
+
+# Security Limits
+LOGIN_RATE_LIMIT_PER_MINUTE=10
+REGISTER_RATE_LIMIT_PER_MINUTE=5
+RESET_RATE_LIMIT_PER_MINUTE=5
+REFRESH_RATE_LIMIT_PER_MINUTE=30
+MESSAGE_RATE_LIMIT_PER_MINUTE=30
+DUPLICATE_MESSAGE_COOLDOWN_SECONDS=10
+
+# Dev/Test utility
+CELERY_TASK_ALWAYS_EAGER=false