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/yuv4mpeg.hpp

@@ -0,0 +1,53 @@
+// Copyright (c) 2025 Hans-Kristian Arntzen
+// SPDX-License-Identifier: MIT
+#pragma once
+
+#include <memory>
+#include <string>
+#include <stdio.h>
+#include <stddef.h>
+
+class YUV4MPEGFile
+{
+public:
+	bool open_read(const std::string &path);
+	bool open_write(const std::string &path, const std::string &params);
+	const std::string &get_params() const;
+
+	int get_width() const;
+	int get_height() const;
+
+	bool begin_frame();
+	bool write(const void *pixels, size_t size);
+	bool read(void *pixels, size_t size);
+
+	enum class Format
+	{
+		YUV420P,
+		YUV444P,
+		YUV420P16,
+		YUV444P16
+	};
+
+	Format get_format() const;
+	bool is_full_range() const;
+
+	static int format_to_bytes_per_component(Format format);
+	static bool format_has_subsampling(Format format);
+
+	int get_frame_rate_num() const;
+	int get_frame_rate_den() const;
+
+private:
+	enum class Mode { Read, Write };
+	bool open(const std::string &path, Mode mode);
+	struct FileDeleter { void operator()(FILE *f) { if (f) fclose(f); } };
+	std::unique_ptr<FILE, FileDeleter> file;
+	int width = 0, height = 0;
+	int frame_rate_num = 60, frame_rate_den = 1;
+	std::string params;
+	Mode mode = {};
+	Format format = {};
+	bool full_range = false;
+	float unorm_scale = 1.0f;
+};