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>

migrations/1791676907.sh

@@ -0,0 +1,10 @@
+echo "Let a lone Shift switch out of an input method and back"
+
+# An earlier migration wrote this list empty. Fill only that empty list: a
+# missing one already falls back to Fcitx's Shift_L, and a filled one is the
+# user's choice.
+config="${XDG_CONFIG_HOME:-$HOME/.config}/fcitx5/config"
+if [[ -f $config ]] && awk '/^\[Hotkey\/AltTriggerKeys\]$/ { in_list = 1; found = 1; next } /^\[/ { in_list = 0 } in_list && /=/ { filled = 1 } END { exit !(found && !filled) }' "$config"; then
+  sed -i --follow-symlinks '/^\[Hotkey\/AltTriggerKeys\]$/a 0=Shift_L' "$config"
+  busctl --user call org.fcitx.Fcitx5 /controller org.fcitx.Fcitx.Controller1 ReloadConfig 2>/dev/null || true
+fi