fix: improve agent output schema, tool descriptions, and shutdown robustness

- Rename status→outputType, responded/silent→message/log for clarity
- Remove scheduled task special-casing: userMessage now sent for all contexts
- Update schema, tool, and CLAUDE.md descriptions to be clear and
  non-contradictory about communication mechanisms
- Use full tool name mcp__nanoclaw__send_message in docs
- Change schedule_task target_group to accept JID instead of folder name
- Only show target_group_jid parameter to main group agents
- Add defense-in-depth sanitization and error callback to exec() in shutdown
- Use "user or group" consistently (supports both 1:1 and group chats)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/container-runner.ts

@@ -41,7 +41,7 @@ export interface ContainerInput {
 }
 
 export interface AgentResponse {
-  status: 'responded' | 'silent';
+  outputType: 'message' | 'log';
   userMessage?: string;
   internalLog?: string;
 }