Extract config and types into separate files, clean up index.ts

- src/config.ts: configuration constants
- src/types.ts: TypeScript interfaces
- src/index.ts: remove section comments, streamline code

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/config.ts

@@ -0,0 +1,8 @@
+export const ASSISTANT_NAME = process.env.ASSISTANT_NAME || 'Andy';
+export const POLL_INTERVAL = 2000;
+export const STORE_DIR = './store';
+export const GROUPS_DIR = './groups';
+export const DATA_DIR = './data';
+
+export const TRIGGER_PATTERN = new RegExp(`^@${ASSISTANT_NAME}\\b`, 'i');
+export const CLEAR_COMMAND = '/clear';