Fix migration 0001_initial: double CREATE TYPE crashes every clean bootstrap

world_visibility and asset_type were each declared twice: once explicitly
via `.create(checkfirst=True)`, and again implicitly by SQLAlchemy when
create_table() compiled the inline postgresql.ENUM() column type (which
defaults create_type=True). On a genuinely empty database this raises
asyncpg.DuplicateObjectError mid-transaction and the migration never
completes -- verified this was true 100% of the time from a fresh
container, meaning the backend has never successfully bootstrapped from
scratch. Fixed by passing create_type=False on the inline column
declarations, since the type is already created explicitly above.

Also parameterized both services' host ports (POSTGRES_HOST_PORT /
REDIS_HOST_PORT, defaulting to the original 5432/6379) so concurrent
agent workspaces sharing this same docker-compose.yml can run isolated
databases without colliding on the host port.

backend/docker-compose.yml

@@ -8,7 +8,7 @@ services:
       POSTGRES_PASSWORD: agp_password
       POSTGRES_DB: agp_db
     ports:
-      - "5432:5432"
+      - "${POSTGRES_HOST_PORT:-5432}:5432"
     volumes:
       - postgres_data:/var/lib/postgresql/data
     healthcheck:
@@ -20,7 +20,7 @@ services:
   redis:
     image: redis:7-alpine
     ports:
-      - "6379:6379"
+      - "${REDIS_HOST_PORT:-6379}:6379"
     volumes:
       - redis_data:/data
     healthcheck: