Add overlay gamepad support for keyboard-only mode (#17)

changes/controller-overlay-support.md

@@ -0,0 +1,7 @@
+type: added
+area: overlay
+
+- Added Chrome Gamepad API controller support for keyboard-only overlay mode, including configurable logical bindings for lookup, mining, popup navigation, Yomitan audio, mpv pause, d-pad fallback navigation, and slower smooth popup scrolling.
+- Added `Alt+C` controller selection and `Alt+Shift+C` controller debug modals, with preferred controller persistence and live raw input inspection.
+- Added a transient in-overlay controller-detected indicator when a controller is first found.
+- Fixed stale keyboard-only token highlight cleanup when keyboard-only mode turns off or the Yomitan popup closes.