fix: propagate desktop portal request errors to avoid startup hang on KDE Wayland

[Branrir]

Problem

On KDE Plasma Wayland, Kando fails to start. xdg-desktop-portal-kde rejects the global-shortcuts CreateSession call with DBusError: An app id is required, producing an unhandled promise rejection and hanging the app during initialization:

(node:13350) UnhandledPromiseRejectionWarning: DBusError: An app id is required

Root cause

In makeRequest (desktop-portal.ts), the callback fired the D-Bus call (e.g. CreateSession) but ignored the returned promise. When the portal rejected instead of replying with a Response signal, the error was never propagated — so makeRequest waited forever, hanging isAvailable() → init() and never opening the window. The try/catch in connectImpl meant to handle this never got the chance to fire.

Fix

• makeRequest now propagates the underlying D-Bus call's rejection (and removes its message listener) instead of waiting indefinitely.
• The portal callbacks in global-shortcuts.ts and remote-desktop.ts now return their D-Bus call promises so rejections reach makeRequest.

With this, a failed portal request rejects cleanly, connectImpl's catch runs, and the KDE backend falls back to its KWin-scripting method as intended — the app starts normally.

Testing

• npm run tscheck, eslint, and prettier all pass.
• Verified Kando launches on KDE Plasma Wayland.

Related issue
#1412

[Schneegans]

Thanks a lot! Maybe we can even fix the root cause for this (I added a comment in #1412). Yet I'll merge this anyways since it seems to be a good idea 😄