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/pyrowave_decoder.hpp

@@ -0,0 +1,47 @@
+// Copyright (c) 2025 Hans-Kristian Arntzen
+// SPDX-License-Identifier: MIT
+#pragma once
+
+#include <memory>
+#include <stddef.h>
+#include <stdint.h>
+#include "pyrowave_config.hpp"
+
+namespace Vulkan
+{
+class Device;
+class ImageView;
+class CommandBuffer;
+}
+
+namespace PyroWave
+{
+class Decoder
+{
+public:
+	Decoder();
+	~Decoder();
+
+	// Fragment path is optimized for typical mobile GPUs which have weak compute support.
+	// iDWT is instead computed entirely in traditional render passes and fragment shaders.
+	// This path is *not* recommended for desktop-class chips.
+	bool init(Vulkan::Device *device, int width, int height,
+	          ChromaSubsampling chroma, bool fragment_path = false);
+
+	static bool device_prefers_fragment_path(Vulkan::Device &device);
+
+	void clear();
+	bool push_packet(const void *data, size_t size);
+
+	// If fragment path is enabled, the command buffer must support graphics operations.
+	// To synchronize, synchronize with COLOR_OUTPUT / COLOR_ATTACHMENT_WRITE / COLOR_ATTACHMENT_OPTIMAL.
+	// Views must be created with VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT.
+	bool decode(Vulkan::CommandBuffer &cmd, const ViewBuffers &views);
+
+	bool decode_is_ready(bool allow_partial_frame) const;
+
+private:
+	struct Impl;
+	std::unique_ptr<Impl> impl;
+};
+}