Add native self-hosted instance connection to fluxer_desktop

Trimmed monorepo checkout (fluxer_desktop + packages/voice_engine_v2 +
tools/ci) with a "Connect to a Different Server" menu item and popout
that lets the desktop app switch to any self-hosted Fluxer instance,
plus fixes for well-known discovery on single-domain self-hosted
deployments and a false-positive ERR_ABORTED on same-origin client
redirects during the switch. Defaults to chat.fluxr.chat and uses an
isolated userData directory from the official build.

fluxer_desktop/native/mac-clipboard/index.d.ts

@@ -0,0 +1,4 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+export declare const writeFileReferenceToClipboard: ((filePath: string) => Promise<void>) | null;
+export declare const loadError: Error | null;