Move infra/ content to doc/deployment.md; delete infra/ directory

docker-compose.yml lives in infra repo; deployment docs belong in doc/.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

infra/docker-compose.yml

@@ -1,16 +0,0 @@
-services:
-  postgres:
-    image: postgres:16-alpine
-    restart: unless-stopped
-    ports:
-      - "5433:5432"
-    environment:
-      POSTGRES_USER: ${POSTGRES_USER:-postgres}
-      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD:?POSTGRES_PASSWORD is required}
-    volumes:
-      - /volume2/docker/shared/pgdata:/var/lib/postgresql/data
-    healthcheck:
-      test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER:-postgres}"]
-      interval: 5s
-      timeout: 5s
-      retries: 5