Reset the terminal before opening the LXC shell

Write ESC c, the sequence `reset` sends, inside suspend() right before
ssh. The container shell then starts on a clean screen with no
leftover TUI terminal modes. It runs locally, so the container does
not need `reset` installed and `pct enter` is unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/cv4pve_tui/app.py

@@ -1,6 +1,7 @@
 """Textual app for managing Proxmox guests through cv4pve-cli."""
 
 import subprocess
+import sys
 
 from textual import work
 from textual.app import App, ComposeResult, SuspendNotSupported
@@ -358,6 +359,7 @@ class GuestApp(App):
         try:
             with self.suspend():
                 try:  # inside: Textual's suspend() skips the resume if its body raises
+                    _reset_terminal()
                     code = subprocess.run(cmd, check=False).returncode
                 except OSError as exc:
                     error = _message(exc)
@@ -426,6 +428,12 @@ class GuestApp(App):
         self._start_job(guest, "edit", job)
 
 
+def _reset_terminal() -> None:
+    """Full terminal reset (ESC c, what `reset` sends): clean screen, no leftover TUI modes."""
+    sys.stdout.write("\033c")
+    sys.stdout.flush()
+
+
 def _scaled(value, unit: int):
     return "-" if value is None else round(value / unit)