fix: terminal resize propagation and redraw

- Frontend: Add ResizeObserver with dimension tracking for accurate resize detection
- Frontend: Fix cleanup function to properly disconnect ResizeObserver
- Frontend: Use CSS grid for terminal wrapper layout
- Backend: Add duplicate dimension check to avoid unnecessary resizes
- Backend: Ensure stty command is sent correctly to container shell

apps/api/src/services/terminal_session.py

@@ -142,6 +142,11 @@ class TerminalSession:
         if self._closed:
             logger.warning("Cannot resize: session is closed")
             return
+        
+        # Only resize if dimensions actually changed
+        if cols == self._cols and rows == self._rows:
+            return
+            
         self._cols = cols
         self._rows = rows
         logger.info(f"resize() called for session {self.session_id}: {cols}x{rows}")