feat(host): vendor PyroWave + minimal Granite subset as crates/pyrowave-sys

Phase 0 of design/pyrowave-codec-plan.md — the opt-in wired-LAN ultra-low-
latency codec. Vendored at upstream 509e4f88 (API 0.4.0, Granite 44362775,
volk + vulkan-headers pins in PUNKTFUNK-VENDOR.txt), pruned to the 6.6 MB
the standalone no-renderer build needs; scripts/vendor-pyrowave.sh
reproduces the tree (a pin bump is protocol-affecting, plan §4.2).

build.rs drives the wrapper CMakeLists (static archives incl. a static
C-API lib upstream only ships shared) + bindgen over pyrowave.h; Linux and
Windows only, empty stub elsewhere (Apple gets a native Metal port, §4.7).
Offline-safe by construction: no network, no system lib, vendored Vulkan
headers — same model as the opus dep (flatpak builder has no network).

Phase-0 validation on .21 (RTX 5070 Ti, driver 610.43.03):
- upstream pyrowave-c-test + interop test (incl. dmabuf/DRM-modifier
  Vulkan<->Vulkan) pass, from the pristine AND the pruned tree
- GPU kernel times at ~1.6 bpp noise: encode/decode 0.090/0.042 ms @800p,
  0.146/0.067 @1080p, 0.226/0.103 @1440p, 0.477/0.201 @4K — order of
  magnitude under NVENC's 1-2 ms retrieve, CBR lands within ~100 B of
  target
- cargo test -p pyrowave-sys green (static link + API-version pin check)

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

crates/pyrowave-sys/vendor/pyrowave/shaders/dwt_quant_scale.h

@@ -0,0 +1,21 @@
+// Copyright (c) 2025 Hans-Kristian Arntzen
+// SPDX-License-Identifier: MIT
+#ifndef DWT_QUANT_SCALE_H_
+#define DWT_QUANT_SCALE_H_
+
+float decode_quant_scale(uint code)
+{
+	// Minimum scale: 0.25
+	// Maximum scale: ~2.2
+	return float(code) / 8.0 + 0.25;
+}
+
+const uint ENCODE_QUANT_IDENTITY = 6;
+
+uint encode_quant_scale(float scale)
+{
+	// Round the quant scale FP up so that the quantizer scale effectively rounds down.
+	return uint(ceil((scale - 0.25) * 8.0));
+}
+
+#endif