feat(oak_bridge): macOS wgpu Metal texture to IOSurface CVPixelBuffer bridge

W3 of the oak task list. SurfaceBridge wraps an engine wgpu (Metal) texture
into an IOSurface-backed CVPixelBuffer for gpui's Surface element: a reused
pixel buffer created with kCVPixelBufferIOSurfacePropertiesKey +
MetalCompatibility, aliased to a Metal texture via gpui_media's
CVMetalTextureCache, with a GPU-to-GPU MTLBlitCommandEncoder copy (a
device.poll(Wait) before the blit keeps the v1 path correct and
synchronous). A CPU readback fallback (stage_readback/finish_readback)
works on any backend. The surface_bridge demo (demo feature) streams a
moving test pattern through the bridge into a window and prints FPS;
smoke-verified on macOS at 1280x720. Windows/Linux paths are left for a
follow-up (noted in docs/zh). 2 tests pass.

Cargo.lock

@@ -4006,6 +4006,21 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "oak_bridge"
+version = "0.1.0"
+dependencies = [
+ "anyhow",
+ "core-foundation 0.10.0",
+ "core-video",
+ "gpui",
+ "gpui_media",
+ "gpui_platform",
+ "metal",
+ "pollster 0.4.0",
+ "wgpu",
+]
+
 [[package]]
 name = "objc"
 version = "0.2.7"