fix: replace Ctrl-S confirm with Ctrl-G in Certificate Details form

Ctrl-S (0x13) is the XOFF flow-control character; terminals intercept it
before curses sees it, causing output suspension in Konsole and others.
Replaced with Ctrl-G (0x07 / BEL) which has no terminal-level meaning.
Updated hint bar and test stub accordingly.

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

tests/test_dialogs.py

@@ -8,6 +8,7 @@ import curses as _curses
 # Stub curses constants before importing the module under test, mirroring
 # what test_widgets.py does for InputField's dependencies.
 _curses.color_pair   = lambda x: 0
+_curses.curs_set     = lambda x: None
 _curses.A_UNDERLINE  = 0
 _curses.A_BOLD       = 0
 _curses.KEY_BACKSPACE = 263