fix(backend): standardize microservice host/port configuration

- Change agentgenerator_host default from empty string to "localhost"
  - Consistent with other client services (rabbitmq, redis, clamav)
  - Fixes "service_not_configured" error when only port is set
- Change agentgenerator_port default from 8000 to 8009
  - Avoids conflict with Kong gateway (port 8000)
  - Follows sequential port allocation (8001-8008 already in use)
- Add AGENTGENERATOR_HOST to .env.default for clarity

This standardization ensures:
1. Consistent host naming across all microservice client configurations
2. No port conflicts with Kong or other services
3. Agent Generator service works out of the box when enabled

autogpt_platform/backend/.env.default

@@ -192,3 +192,8 @@ POSTHOG_HOST=https://eu.i.posthog.com
 
 # Other Services
 AUTOMOD_API_KEY=
+
+# Agent Generator Service
+# The Agent Generator microservice handles AI-powered agent creation from natural language
+AGENTGENERATOR_HOST=localhost
+AGENTGENERATOR_PORT=8009

autogpt_platform/backend/backend/util/settings.py

@@ -364,11 +364,11 @@ class Config(UpdateTrackingModel["Config"], BaseSettings):
     )
 
     agentgenerator_host: str = Field(
-        default="",
-        description="The host for the Agent Generator service (empty to use built-in)",
+        default="localhost",
+        description="The host for the Agent Generator service",
     )
     agentgenerator_port: int = Field(
-        default=8000,
+        default=8009,
         description="The port for the Agent Generator service",
     )
     agentgenerator_timeout: int = Field(