feat(presenter): VAAPI dmabuf → Vulkan zero-copy import + CSC pass (phase 2)

The decoder's NV12 dmabuf imports per-plane (R8 + GR88, explicit DRM
format modifier, dedicated dup'd-fd import, FOREIGN→graphics acquire)
and a fullscreen-triangle render pass converts it into the presenter's
video image with the CICP-driven coefficients ported from video_gl.rs
(same tests, plus a rows-vs-matrix agreement check). SPIR-V is committed
(shaders/build.sh regenerates) so builds and CI need no toolchain. The
import extension set is probed at device creation; unsupported boxes and
3-failure streaks demote the decoder to software via the existing
force_software contract. The session binary now honors the Settings
decoder preference instead of forcing software.

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

crates/pf-presenter/shaders/fullscreen.vert

@@ -0,0 +1,14 @@
+// The bufferless fullscreen triangle (same trick as the GL presenter's gl_VertexID
+// geometry). Vulkan clip space: y=-1 is the TOP, so uv (0,0) lands on the top-left —
+// which is exactly where the video's row 0 lives. No flip anywhere.
+//
+// Regenerate: shaders/build.sh (committed .spv, no build-time toolchain).
+#version 450
+
+layout(location = 0) out vec2 v_uv;
+
+void main() {
+    vec2 uv = vec2((gl_VertexIndex << 1) & 2, gl_VertexIndex & 2);
+    v_uv = uv;
+    gl_Position = vec4(uv * 2.0 - 1.0, 0.0, 1.0);
+}