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/rust/benches/baseline.json

@@ -0,0 +1,36 @@
+{
+	"measured_at": "85e057a273fd",
+	"host": "darwin-arm64-apple-silicon",
+	"regression_budget_percent": 5.0,
+	"criterion_args": {
+		"warm_up_time_sec": 2,
+		"measurement_time_sec": 5
+	},
+	"benches": {
+		"routing/default_sink_playback_stream": {
+			"median_ns": 41.6,
+			"low_ns": 41.327,
+			"high_ns": 41.862
+		},
+		"ring/fill_drain_1024": {
+			"median_ns": 3866.6,
+			"low_ns": 3844.2,
+			"high_ns": 3891.2
+		},
+		"audio/mono_to_stereo_1s": {
+			"median_ns": 1119800.0,
+			"low_ns": 1112300.0,
+			"high_ns": 1128900.0
+		},
+		"evdev/keymap_roundtrip_table": {
+			"median_ns": 11119.0,
+			"low_ns": 11054.0,
+			"high_ns": 11194.0
+		},
+		"mac_process_tree/collect_512_chain": {
+			"median_ns": 48667.0,
+			"low_ns": 48397.0,
+			"high_ns": 48975.0
+		}
+	}
+}