Remove redundant comments throughout codebase

Keep only comments that explain non-obvious behavior or add context
not apparent from reading the code.

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

src/auth.ts

@@ -28,7 +28,6 @@ async function authenticate(): Promise<void> {
 
   const { state, saveCreds } = await useMultiFileAuthState(AUTH_DIR);
 
-  // Check if already authenticated
   if (state.creds.registered) {
     console.log('✓ Already authenticated with WhatsApp');
     console.log('  To re-authenticate, delete the store/auth folder and run again.');