fix(overlay): reload imported mpv keys after mpv connects (#278)

* fix(overlay): reload imported mpv keys after mpv connects

The overlay fetched mpv's input-bindings before SubMiner connected to mpv,
cached an empty list, and never refetched because the connect-time refresh
only broadcast session bindings when their compiled signature changed. Keys
from input.conf and mpv defaults (9/0 volume, m mute) then did nothing while
the overlay had focus, most often in mpv.backend x11 mode.

Main now emits mpv-input-bindings:changed whenever the discovered mpv key
set or client changes, and the renderer refreshes its imported keys on it.

* fix(overlay): subscribe to mpv key changes before initial discovery

The renderer registered the mpv-input-bindings:changed listener only after awaiting setupMpvInputForwarding and several other startup calls. If mpv connected in that window, the event was dropped and the imported mpv keys stayed empty.

src/renderer/handlers/keyboard.ts

@@ -1335,6 +1335,9 @@ export function createKeyboardHandlers(
     setupMpvInputForwarding,
     refreshConfiguredShortcuts,
     updateSessionBindings,
+    refreshMpvInputBindings: () => {
+      void importedMpvBindings.refresh();
+    },
     syncKeyboardTokenSelection,
     handleSubtitleContentUpdated,
     togglePrimarySubtitleBarVisibility,