fix: clear screen initialization blank space after attaching

GNU screen creates blank space at the top when initializing sessions.
This is now handled after attaching to the screen:

- Claude sessions: emit clearTerminal event after 100ms, client clears xterm
- Shell sessions: send 'clear' command after 100ms

Also updates CLAUDE.md with documentation of the fix.

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

src/screen-manager.ts

@@ -52,7 +52,9 @@ export class ScreenManager extends EventEmitter {
     const screenName = `claudeman-${sessionId.slice(0, 8)}`;
 
     // Create screen in detached mode with the appropriate command
-    const cmd = mode === 'claude' ? 'claude --dangerously-skip-permissions' : '$SHELL';
+    const cmd = mode === 'claude'
+      ? 'claude --dangerously-skip-permissions'
+      : '$SHELL';
 
     try {
       // Start screen in detached mode