revert: remove SIGWINCH signal that caused connection loops

Sending SIGWINCH to the docker exec process was crashing/killing it,
which closed the PTY and caused WebSocket 1006 abnormal closure loops.
Reverting to the original TIOCSWINSZ-only approach.

apps/api/src/services/terminal_session.py

@@ -5,7 +5,6 @@ import logging
 import os
 import pty
 import select
-import signal
 import struct
 import fcntl
 import time
@@ -84,7 +83,7 @@ class TerminalSession:
         self.last_activity = time.time()
 
     def _set_terminal_size(self, cols: int, rows: int) -> None:
-        """Set the terminal size using TIOCSWINSZ and signal docker exec."""
+        """Set the terminal size using TIOCSWINSZ."""
         if self._master_fd is None:
             logger.warning("Cannot resize: master_fd is None (session not started)")
             return
@@ -94,15 +93,6 @@ class TerminalSession:
         try:
             fcntl.ioctl(self._master_fd, TIOCSWINSZ, size)
             logger.info(f"Resized PTY to {cols}x{rows} (fd={self._master_fd})")
-            
-            # Send SIGWINCH to docker exec process so it re-reads terminal
-            # size and propagates it to the container's PTY
-            if self.process and self.process.pid:
-                try:
-                    os.kill(self.process.pid, signal.SIGWINCH)
-                    logger.info(f"Sent SIGWINCH to docker exec pid={self.process.pid}")
-                except (OSError, ProcessLookupError) as e:
-                    logger.warning(f"Failed to send SIGWINCH: {e}")
         except (OSError, IOError) as e:
             logger.error(f"Failed to resize PTY: {e}")