feat: double Esc to exit main menu; fix Cryptgeon test for new payload schema

- First Esc in main screen shows "Press Esc again to quit" in footer;
  second Esc exits. Any other key resets the pending state.
- Update test_posts_to_correct_endpoint to expect contents as base64 string
  and presence of meta field, matching the updated Cryptgeon API payload.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

openvpncertupdate.py

@@ -745,6 +745,7 @@ def show_main_screen(
     n_items  = n_certs + len(_MENU_ITEMS)
     checked: set[str] = set(initial_checked) if initial_checked else set()
     cursor = clamp(initial_cursor, 0, max(0, n_items - 1))
+    esc_pending = False
 
     def is_cert(idx):  return idx < n_certs
     def menu_item(idx): return _MENU_ITEMS[idx - n_certs] if idx >= n_certs else None
@@ -763,7 +764,10 @@ def show_main_screen(
             pass
 
         # Footer hint
-        hint = " ↑↓:Navigate  Space:Check  Enter:Confirm  R:Revoke  A:Toggle view  Q:Quit"
+        if esc_pending:
+            hint = " Press Esc again to quit"
+        else:
+            hint = " ↑↓:Navigate  Space:Check  Enter:Confirm  R:Revoke  A:Toggle view  Q:Quit"
         try:
             stdscr.addstr(sh - 1, 0, hint[:sw], curses.color_pair(COLOR_DISABLED))
         except curses.error:
@@ -810,6 +814,14 @@ def show_main_screen(
         draw()
         key = stdscr.getch()
 
+        if key == 27:  # Esc
+            if esc_pending:
+                return ScreenResult(action=Action.EXIT)
+            esc_pending = True
+            continue
+
+        esc_pending = False
+
         if key in (ord("q"), ord("Q")):
             return ScreenResult(action=Action.EXIT)