refactor: use YAML map for gateway environment variables instead of string parsing

Benefits:
- More idiomatic configuration format for Home Assistant add-ons
- config.yaml: Change default from empty string to empty YAML map
- config.yaml: Update schema type from str? to map(str)?
- config.yaml: Improve documentation to explain YAML map usage
- run.sh: Parse JSON object from jq using to_entries instead of semicolon splitting
- oc_config_helper.py: Accept JSON string and parse as dict instead of semicolon-separated values
- Better error handling for invalid JSON
- Cleaner and more maintainable parsing logic

This allows users to configure environment variables more naturally:
  gateway_env_vars:
    OPENAI_API_KEY: sk-abc123
    SERVICE_URL: https://api.example.com

openclaw_assistant/run.sh

@@ -52,7 +52,7 @@ GATEWAY_PORT=$(jq -r '.gateway_port // 18789' "$OPTIONS_FILE")
 ENABLE_OPENAI_API=$(jq -r '.enable_openai_api // false' "$OPTIONS_FILE")
 ALLOW_INSECURE_AUTH=$(jq -r '.allow_insecure_auth // false' "$OPTIONS_FILE")
 FORCE_IPV4_DNS=$(jq -r '.force_ipv4_dns // false' "$OPTIONS_FILE")
-GW_ENV_VARS=$(jq -r '.gateway_env_vars // empty' "$OPTIONS_FILE")
+GW_ENV_VARS=$(jq -c '.gateway_env_vars // {}' "$OPTIONS_FILE")
 
 export TZ="$TZNAME"
 
@@ -150,22 +150,22 @@ export PATH="${PNPM_HOME}:${PATH}"
 
 # Export gateway environment variables from add-on config
 # These are user-defined variables that should be available to the gateway process
-if [ -n "$GW_ENV_VARS" ]; then
+if [ "$GW_ENV_VARS" != "{}" ] && [ -n "$GW_ENV_VARS" ]; then
   echo "INFO: Setting gateway environment variables from add-on config..."
   env_count=0
   max_env_vars=50
   max_var_name_size=255
   
+  # Parse JSON object and export each key=value pair
   while IFS='=' read -r key value; do
-    # Skip empty lines
+    # Skip empty lines and trim whitespace
+    key=$(echo "$key" | xargs)
+    value=$(echo "$value" | xargs)
+    
     if [ -z "$key" ]; then
       continue
     fi
     
-    # Trim whitespace
-    key=$(echo "$key" | xargs)
-    value=$(echo "$value" | xargs)
-    
     # Validate variable name format
     if ! [[ "$key" =~ ^[A-Za-z_][A-Za-z0-9_]*$ ]]; then
       echo "WARN: Invalid environment variable name: '$key' (must start with letter/underscore, skip)"
@@ -187,7 +187,7 @@ if [ -n "$GW_ENV_VARS" ]; then
     export "$key=$value"
     ((env_count++))
     echo "INFO: Exported gateway env var: $key"
-  done < <(echo "$GW_ENV_VARS" | tr ';' '\n')
+  done < <(echo "$GW_ENV_VARS" | jq -r 'to_entries[] | "\(.key)=\(.value)"')
   
   if [ $env_count -gt 0 ]; then
     echo "INFO: Successfully exported $env_count gateway environment variable(s)"