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/platform-info/build.rs

@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+fn main() {
+    napi_build::setup();
+
+    if std::env::var("CARGO_CFG_TARGET_OS").as_deref() == Ok("macos") {
+        println!("cargo:rustc-link-lib=framework=CoreGraphics");
+    }
+}