feat(client): PyroWave decode backend on the presenter's device (Phase 2b, part 1)

The presenter's device creation now probes + enables the PyroWave
compute feature set alongside the Vulkan Video probe (shaderInt16,
storageBuffer8BitAccess, subgroup size control — gated on support,
harmless when unused) and exports the facts through VulkanDecodeDevice
(pyrowave_decode capability + feature bools + apiVersion + the queue-
family shape).

pf-client-core (feature `pyrowave`, Linux): video_pyrowave.rs — the
decoder runs pyrowave compute on the PRESENTER's own VkDevice, zero
interop (plan §4.5): pinned content-equivalent create-info
reconstruction satisfies pyrowave 0.4.0's lifetime rule without
refactoring the presenter's creation; queue access rides the existing
device-wide QueueLock (the FFmpeg/Skia contract); decode records into
our command buffer, fence-synchronous (sub-ms), into a 4-deep ring of
3xR8 plane sets (decode REQUIRES storage usage + identity swizzles, so
the encoder's RG8 trick doesn't apply). Backend::PyroWave +
DecodedImage::PyroWave + Decoder::new_pyrowave + decodable_codecs_for
(advertisement gated on the device probe) wired through the decode
dispatch; no demote ladder (nothing else decodes it — fallback is
session renegotiation, plan §4.6).

Still to come for a live session: the presenter's planar-CSC render
path for the new variant, pump/shell opt-in (preferred_codec) wiring,
and the on-glass .21 run.

Validated on .21: pf-client-core + pf-presenter compile with and
without the feature, clippy clean, 26 client-core tests green.

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

crates/pf-client-core/Cargo.toml

@@ -40,6 +40,11 @@ tracing = "0.1"
 [target.'cfg(target_os = "linux")'.dependencies]
 pipewire = "0.9"
 sdl3 = { version = "0.18", features = ["hidapi"] }
+# PyroWave decode (the opt-in wired-LAN wavelet codec, design/pyrowave-codec-plan.md
+# §4.5) — pure Vulkan compute on the presenter's shared device. `ash` only wraps the
+# presenter's existing raw handles (same pinned version as pf-presenter).
+pyrowave-sys = { path = "../pyrowave-sys", optional = true }
+ash = { version = "0.38", optional = true }
 
 [target.'cfg(windows)'.dependencies]
 wasapi = "0.23"
@@ -57,3 +62,8 @@ windows = { git = "https://github.com/microsoft/windows-rs", rev = "a4f7b2cb7c63
     # method itself is feature-gated behind this.
     "Win32_Security",
 ] }
+
+[features]
+# PyroWave client decode — OFF by default (the flatpak/default builds stay unchanged);
+# the Linux session client turns it on together with the host-side feature.
+pyrowave = ["dep:pyrowave-sys", "dep:ash"]