fix: flush stdin after curses/terminal menus to prevent escape sequence leakage (#7167)

After curses.wrapper() or simple_term_menu exits, endwin() restores the
terminal but does NOT drain the OS input buffer. Leftover escape-sequence
bytes from arrow key navigation remain buffered and get silently consumed
by the next input()/getpass.getpass() call.

This caused a user-reported bug where selecting Z.AI/GLM as provider wrote
^[^[ (two ESC chars) into .env as the API key, because the buffered escape
bytes were consumed by getpass before the user could type anything.

Fix: add flush_stdin() helper using termios.tcflush(TCIFLUSH) and call it
after every curses.wrapper() and simple_term_menu .show() return across all
interactive menu sites:
- hermes_cli/curses_ui.py (curses_checklist)
- hermes_cli/setup.py (_curses_prompt_choice)
- hermes_cli/tools_config.py (_prompt_choice)
- hermes_cli/auth.py (_prompt_model_selection)
- hermes_cli/main.py (3 simple_term_menu usages)

hermes_cli/auth.py

@@ -2616,6 +2616,8 @@ def _prompt_model_selection(
             title=effective_title,
         )
         idx = menu.show()
+        from hermes_cli.curses_ui import flush_stdin
+        flush_stdin()
         if idx is None:
             return None
         print()