refactor(schemas): rename Agent* schemas and WS frame types to Scout*
Rename all Pydantic models referring to the scout subsystem:
AgentConfig → ScoutConfig, ContentTypeConfig → ScoutContentTypeConfig,
AgentCatalogItem → ScoutCatalogItem, AgentCreationCheckRequest/Response →
ScoutCreationCheckRequest/Response, AgentTriggerRequest → ScoutTriggerRequest,
AgentRunLogResponse → ScoutRunLogResponse.
LLM-helper agent schemas in app/agents/* are untouched.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>