refactor: remove env vars from oc_config_helper, keep validation in run.sh

Environment variables are fully handled by run.sh:
- run.sh reads gateway_env_vars from options.json
- run.sh validates variable names (alphanumeric + underscore)
- run.sh enforces max 50 variables and 255 char name limit
- run.sh exports to process environment

oc_config_helper.py now only manages gateway config (mode, port, bind).

Removes:
- env_vars parameter from apply_gateway_settings()
- All env var parsing and validation from Python helper
- MAX_ENV_VARS constants
- env_vars CLI argument

openclaw_assistant/run.sh

@@ -400,7 +400,7 @@ fi
 
 if [ -f "$OPENCLAW_CONFIG_PATH" ]; then
   if [ -f "$HELPER_PATH" ]; then
-    if ! python3 "$HELPER_PATH" apply-gateway-settings "$GATEWAY_MODE" "$GATEWAY_BIND_MODE" "$GATEWAY_PORT" "$ENABLE_OPENAI_API" "$ALLOW_INSECURE_AUTH" "$GW_ENV_VARS"; then
+    if ! python3 "$HELPER_PATH" apply-gateway-settings "$GATEWAY_MODE" "$GATEWAY_BIND_MODE" "$GATEWAY_PORT" "$ENABLE_OPENAI_API" "$ALLOW_INSECURE_AUTH"; then
       rc=$?
       echo "ERROR: Failed to apply gateway settings via oc_config_helper.py (exit code ${rc})."
       echo "ERROR: Gateway configuration may be incorrect; aborting startup."