feat: session source in session_meta and an Automated sidebar folder (#40)

Co-authored-by: Alice <alice@prismshadow.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

packages/docs/content/omni-message.en.md

@@ -41,6 +41,7 @@ interface SessionMetaPayload {
   thinking_level: string;                 // "default" when unconfigured
   agent_state: string;                    // absolute path of the Agent State
   workspace: string;                      // absolute path of the Workspace
+  source?: "subagent" | "schedule";       // session origin; absent = user-created
 }
 
 interface ToolDefinition {