fix: send stty resize on every resize with hidden command output

Backend:
- Remove _stty_sent guard to send stty on EVERY resize
- Use stty -echo to hide command, then delete the command line with ANSI escapes
- Change log level from info to debug

Frontend:
- Add window resize listener as fallback to ResizeObserver
- 250ms debounce to avoid excessive refits
- Proper cleanup on unmount

apps/api/src/services/terminal_session.py

@@ -154,12 +154,14 @@ class TerminalSession:
         
         # Docker exec doesn't forward PTY resize to the container process,
         # so we need to explicitly set the size inside the container shell.
-        # Only do this on the first resize to avoid interfering with user input.
-        if not getattr(self, '_stty_sent', False):
-            self._stty_sent = True
-            stty_cmd = f"stty cols {cols} rows {rows}\n".encode()
-            await self.write_input(stty_cmd)
-            logger.info(f"Sent stty command to container for session {self.session_id}: {cols}x{rows}")
+        # Send on every resize so the container shell always matches the frontend.
+        # Use stty -echo to prevent the command from being visible, then clear the line.
+        stty_cmd = (
+            f"stty -echo; stty cols {cols} rows {rows}; stty echo\n"
+            f"\x1b[A\x1b[M"  # Move up 1 line and delete it (clears the stty command)
+        ).encode()
+        await self.write_input(stty_cmd)
+        logger.debug(f"Sent stty resize to container for session {self.session_id}: {cols}x{rows}")
 
     async def reset(self) -> None:
         """Reset the session by killing the process and clearing state."""