Switch out of an input method and back with a lone Shift (#14975)

* Switch out of an input method and back with a lone Shift

Fcitx's alternate trigger only acts while an engine like Pinyin is or was
active, so Shift + letter and plain Latin typing are unaffected. It needs
Shift releases intact, which the both-Shifts Caps Lock option prevented.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* Follow XDG_CONFIG_HOME in the Shift migration and test it

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

default/input-methods/configure.py

@@ -108,7 +108,6 @@ def defaults(config_home, fresh=False):
         stock_lists = {
           "Hotkey/ActivateKeys": {"0": "Hangul_Hanja"},
           "Hotkey/DeactivateKeys": {"0": "Hangul_Romaja"},
-          "Hotkey/AltTriggerKeys": {"0": "Shift_L"},
           "Hotkey/EnumerateGroupForwardKeys": {"0": "Super+space"},
           "Hotkey/EnumerateGroupBackwardKeys": {"0": "Super+Shift+space"},
           "TriggerKey": {"0": "Super+grave", "1": "Super+semicolon"},