feat: add 'both' agent type for shared Claude Code + Codex channels

- AgentType now supports 'both' — runs both agents sequentially
- Each agent gets its own folder suffix (_cc / _codex) for isolated sessions
- Claude Code bot handles message storage for 'both' channels
- Responses routed through the matching bot for each agent type

src/types.ts

@@ -32,7 +32,7 @@ export interface ContainerConfig {
   timeout?: number; // Default: 300000 (5 minutes)
 }
 
-export type AgentType = 'claude-code' | 'codex';
+export type AgentType = 'claude-code' | 'codex' | 'both';
 
 export interface RegisteredGroup {
   name: string;