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/curses_ui.py

@@ -10,6 +10,28 @@ from typing import Callable, List, Optional, Set
 from hermes_cli.colors import Colors, color
 
 
+def flush_stdin() -> None:
+    """Flush any stray bytes from the stdin input buffer.
+
+    Must be called after ``curses.wrapper()`` (or any terminal-mode library
+    like simple_term_menu) returns, **before** the next ``input()`` /
+    ``getpass.getpass()`` call.  ``curses.endwin()`` restores the terminal
+    but does NOT drain the OS input buffer — leftover escape-sequence bytes
+    (from arrow keys, terminal mode-switch responses, or rapid keypresses)
+    remain buffered and silently get consumed by the next ``input()`` call,
+    corrupting user data (e.g. writing ``^[^[`` into .env files).
+
+    On non-TTY stdin (piped, redirected) or Windows, this is a no-op.
+    """
+    try:
+        if not sys.stdin.isatty():
+            return
+        import termios
+        termios.tcflush(sys.stdin, termios.TCIFLUSH)
+    except Exception:
+        pass
+
+
 def curses_checklist(
     title: str,
     items: List[str],
@@ -131,6 +153,7 @@ def curses_checklist(
                     return
 
         curses.wrapper(_draw)
+        flush_stdin()
         return result_holder[0] if result_holder[0] is not None else cancel_returns
 
     except Exception: