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/audio-mix/benches/baseline.json

@@ -0,0 +1,18 @@
+{
+	"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": {
+		"audio_mix_tick/mix_8_sources_1024_samples": {
+			"median_ns": 2103.8,
+			"low_ns": 2091.3,
+			"high_ns": 2117.0,
+			"budget_percent_override": 8.0,
+			"note": "Sub-microsecond mix tick; on Apple Silicon with thermal scaling, observed run-to-run sigma is ~3-4%, so 8% leaves room for noise without hiding 1.5x slowdowns."
+		}
+	}
+}