Show the headset settings panel as its own OpenXR quad layer

The panel was drawn into the eye images, so below a 1.00x OpenXR
resolution its 1440x1080 canvas was minified into a small eye region and
the text became hard to read. It is now submitted as a quad layer of its
own over the scene's projection or menu quad, which the compositor samples
directly at any render scale.

Each backend (D3D12, Windows Vulkan, Quest) makes the panel's swapchain
pair (plus two shared buffers on the Quest) the first time the panel
opens. While it is open, the frame hands Aurora one more stereo target
after the eyes, which the bridge fills with the panel texture or a
transparent image. The panel image follows the eyes' displayed/retained
pairing, so a cancelled frame never shows an unwritten panel. The quad
hangs where the pointer's hits are tested. Aurora leaves the panel out of
the eyes in layer mode, and a backend that cannot make the layer falls
back to drawing it into the eyes.

On the Quest, debug.wiicompiled.panel_layer 0 selects the old path at
run time. Measured there at a race start (render_scale 0.8), the layer
costs nothing while the panel is closed; while it is open, app GPU time is
10.5 ms against 9.7 ms drawn into the eyes, with unchanged frame rates.

The replay tests cover lazy creation, cancelled frames, closed and
unplaced panels, and render-first pacing on D3D12 and Windows Vulkan.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/quest-port.md

@@ -614,6 +614,7 @@ the app:
 | --- | --- |
 | `debug.wiicompiled.vtxpad 0` | Turns the stride padding off, to re-check a driver update |
 | `debug.wiicompiled.validation 1` | Keeps WebGPU validation and robustness on in release builds |
+| `debug.wiicompiled.panel_layer 0` | Draws the headset settings panel into the eye images instead of on its own quad layer (`OPENXR.md`, Settings in the headset); read about once a second, so it can be switched while the panel is open |
 | `debug.wiicompiled.inject <n>:<button>` | Presses `a`, `b`, `x`, `y`, `start`, `up`, `down`, `left` or `right` for 12 XR frames each time `<n>` changes. As a Wii Remote, `x`/`y`/`start` are 1/2/+, the directions push the Nunchuk stick, and `home`, `c` and `z` also exist. `panel` presses the settings panel's button (left Y, or both thumbsticks as a gamepad), opening or closing it (see `OPENXR.md`) |
 | `debug.wiicompiled.fpslog 1` | Logs the game's rendered frame rate every 5 s, with per-frame averages of the producer's waits for the frame worker's DONE and SEALED phases and of the worker's seal, permit wait, prepare and encode stretches. A third line reports the GX thread's command ring (records, waits, busy share). A second line gives the GPU time per frame from timestamp queries on every pass (`mono` native render, `eyeL`/`eyeR` replays, `screen`, `panel`, `efbcopy`, `palette`, `peek`, plus `passes-span` from the first pass begin to the last pass end and `between-passes` for copies and idle gaps). The compositor's `VrApi` log line gives headset FPS, `GPU%`, `CPU%`, clock levels and app GPU time (`App=`) |