feat: implement one-shot modifier keys for mobile terminal

- Redesign useSpecialKeys hook with modifier state tracking
- Add one-shot activation for Ctrl and Alt keys
- Visual feedback: active modifiers shown with yellow highlight
- Fix focusInput to use term.focus() instead of hidden input
- Always refocus terminal after sending any special key
- Add requestAnimationFrame for reliable focus restoration

apps/web/src/components/terminal.tsx

@@ -198,7 +198,7 @@ export const TerminalComponent: React.FC<TerminalProps> = ({
         }
       };
       const focusInput = () => {
-        hiddenInputRef.current?.focus();
+        termRef.current?.focus();
       };
       onTerminalReadyRef.current(sendData, status, focusInput);
     }
@@ -230,7 +230,7 @@ export const TerminalComponent: React.FC<TerminalProps> = ({
         }
       };
       const focusInput = () => {
-        hiddenInputRef.current?.focus();
+        termRef.current?.focus();
       };
       onTerminalReady(sendData, status, focusInput);
     }