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/encoder-ring/tests/ring_skip_dont_block.rs

@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+use fluxer_encoder_ring::{
+    CpuMemcpyBackend, CpuSlotHandle, EncoderInputRing, RING_SIZE, TextureFormat,
+};
+
+fn fill_noop(_: &mut CpuSlotHandle) {}
+
+#[test]
+fn submit_skip_oldest_drops_first_half_when_pushed_twice_capacity() {
+    let mut ring = EncoderInputRing::new(CpuMemcpyBackend::new());
+    ring.initialise(64, 64, TextureFormat::Nv12)
+        .expect("init ring");
+    let capacity = ring.capacity();
+    assert_eq!(capacity, RING_SIZE);
+    assert_eq!(capacity, 8);
+    let total_pushes: u64 = 2 * capacity as u64;
+    for _ in 0..total_pushes {
+        ring.submit_skip_oldest(fill_noop)
+            .expect("skip-oldest accepts every push");
+    }
+    assert_eq!(ring.submitted_count(), total_pushes);
+    assert_eq!(ring.dropped_count(), capacity as u64);
+    assert_eq!(ring.free_count(), 0);
+    let mut observed: Vec<u64> = Vec::with_capacity(capacity);
+    for _ in 0..capacity {
+        let ready = ring.poll_next_ready().expect("ready");
+        observed.push(ready.sequence);
+        ring.release_completed(ready).expect("release");
+    }
+    let expected: Vec<u64> = (capacity as u64 + 1..=total_pushes).collect();
+    assert_eq!(
+        observed, expected,
+        "skip-don't-block kept newest {capacity} frames"
+    );
+    assert_eq!(ring.free_count(), capacity);
+    assert!(ring.poll_next_ready().is_none());
+}
+
+#[test]
+fn submit_skip_oldest_succeeds_when_room_available() {
+    let mut ring = EncoderInputRing::new(CpuMemcpyBackend::new());
+    ring.initialise(64, 64, TextureFormat::Nv12)
+        .expect("init ring");
+    for _ in 0..3 {
+        ring.submit_skip_oldest(fill_noop).expect("submit");
+    }
+    assert_eq!(ring.dropped_count(), 0);
+    assert_eq!(ring.submitted_count(), 3);
+    assert_eq!(ring.free_count(), ring.capacity() - 3);
+}
+
+#[test]
+fn submit_skip_oldest_keeps_metrics_consistent() {
+    let mut ring = EncoderInputRing::new(CpuMemcpyBackend::new());
+    ring.initialise(64, 64, TextureFormat::Nv12)
+        .expect("init ring");
+    for _ in 0..(3 * ring.capacity() as u64) {
+        ring.submit_skip_oldest(fill_noop).expect("submit");
+    }
+    let metrics = ring.metrics();
+    assert_eq!(metrics.submitted_count, 3 * ring.capacity() as u64);
+    assert_eq!(metrics.dropped_count, 2 * ring.capacity() as u64);
+    assert!(metrics.completed_count <= metrics.submitted_count);
+}