feat: implement cross-platform hotkey management and update frontend build infrastructure

internal/xhotkey/asynckey_stub.go

@@ -0,0 +1,8 @@
+//go:build !windows
+
+package hotkey
+
+// AsyncKeyDown is a stub on non-Windows platforms.
+func AsyncKeyDown(vk int) bool {
+	return false
+}

internal/xhotkey/asynckey_windows.go

@@ -0,0 +1,10 @@
+//go:build windows
+
+package hotkey
+
+import "wis-free-v3/internal/xhotkey/internal/win"
+
+// AsyncKeyDown reports whether the virtual key is currently held (high bit of GetAsyncKeyState).
+func AsyncKeyDown(vk int) bool {
+	return win.GetAsyncKeyState(vk)&0x8000 != 0
+}