fix: merge user-provided disallowedTools instead of overwriting (#295)

## Summary

- User-provided `disallowedTools` from `_meta.claudeCode.options` were
silently overwritten by ACP's internal list
- Now merges both lists, following the same pattern used for `hooks` and
`mcpServers`
- Updated `NewSessionMeta` JSDoc to document the merge behavior

Fixes #294

src/acp-agent.ts

@@ -172,6 +172,7 @@ export type NewSessionMeta = {
      * Those parameters will be used and updated to work with ACP:
      *   - hooks (merged with ACP's hooks)
      *   - mcpServers (merged with ACP's mcpServers)
+     *   - disallowedTools (merged with ACP's disallowedTools)
      */
     options?: Options;
   };
@@ -1105,7 +1106,7 @@ export class ClaudeAcpAgent implements Agent {
       options.allowedTools = allowedTools;
     }
     if (disallowedTools.length > 0) {
-      options.disallowedTools = disallowedTools;
+      options.disallowedTools = [...(options.disallowedTools || []), ...disallowedTools];
     }
 
     // Handle abort controller from meta options