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/main.py

@@ -1672,6 +1672,8 @@ def _remove_custom_provider(config):
             title="Select provider to remove:",
         )
         idx = menu.show()
+        from hermes_cli.curses_ui import flush_stdin
+        flush_stdin()
         print()
     except (ImportError, NotImplementedError, OSError, subprocess.SubprocessError):
         for i, c in enumerate(choices, 1):
@@ -1749,6 +1751,8 @@ def _model_flow_named_custom(config, provider_info):
                 title=f"Select model from {name}:",
             )
             idx = menu.show()
+            from hermes_cli.curses_ui import flush_stdin
+            flush_stdin()
             print()
             if idx is None or idx >= len(models):
                 print("Cancelled.")
@@ -1867,6 +1871,8 @@ def _prompt_reasoning_effort_selection(efforts, current_effort=""):
             title="Select reasoning effort:",
         )
         idx = menu.show()
+        from hermes_cli.curses_ui import flush_stdin
+        flush_stdin()
         if idx is None:
             return None
         print()