fix: remove API_PORT from container environment variables

The API_PORT variable was incorrectly included in the container's
environment section. It should only be used for host port mapping
in docker-compose.yml, not passed into the container.

Changes:
- Remove API_PORT from environment section in docker-compose.yml
- Container always uses port 8080 internally (hardcoded in entrypoint.sh)
- API_PORT in .env/.env.example only controls the host-side mapping:
  ports: "${API_PORT:-8080}:8080" (host:container)

Why this matters:
- Prevents confusion about whether API_PORT changes internal port
- Clarifies that entrypoint.sh hardcodes --port 8080
- Simplifies container environment (one less unused variable)
- More explicit about the port mapping behavior

No functional change - the container was already ignoring this variable.

docker-compose.yml

@@ -24,9 +24,6 @@ services:
       - TRADE_HTTP_PORT=8002
       - GETPRICE_HTTP_PORT=8003
 
-      # API Configuration
-      - API_PORT=${API_PORT:-8080}
-
       # Agent Configuration
       - AGENT_MAX_STEP=${AGENT_MAX_STEP:-30}
     ports: