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/power_to_db.comp

@@ -0,0 +1,33 @@
+#version 450
+// Copyright (c) 2025 Hans-Kristian Arntzen
+// SPDX-License-Identifier: MIT
+#extension GL_EXT_samplerless_texture_functions : require
+
+layout(set = 0, binding = 0) uniform texture2D uTex;
+layout(set = 0, binding = 1) writeonly uniform image2D uImage;
+
+layout(local_size_x = 8, local_size_y = 8) in;
+
+float power_to_db(float p)
+{
+    return max(10.0 * log2(p) / log2(10.0), -100.0);
+}
+
+void main()
+{
+    float input_power = 0.0;
+    const int Stride = 8;
+    for (int y = 0; y < Stride; y++)
+    {
+        for (int x = 0; x < Stride; x++)
+        {
+            if (any(notEqual(ivec4(gl_GlobalInvocationID.xy, x, y), ivec4(0))))
+            {
+                vec2 c = texelFetch(uTex, ivec2(gl_GlobalInvocationID.xy) * Stride + ivec2(x, y), 0).xy;
+                input_power += dot(c, c);
+            }
+        }
+    }
+
+    imageStore(uImage, ivec2(gl_GlobalInvocationID.xy), vec4(power_to_db(input_power)));
+}