M2(Vulkan): implicit capture layer (coop_vk_layer) + chain dispatch + env test

A real chain-aware Vulkan implicit layer the loader inserts at vkCreateInstance
-- the reliable early-presence path for games that init Vulkan immediately,
which the inline-hook vk_hook can't catch. It intercepts vkCreateInstance /
Device / CreateSwapchainKHR / QueuePresentKHR via proper layer-chain dispatch
and does the same read-back capture (vkCmdCopyImageToBuffer -> swizzle ->
hook-owned D3D11 shared texture, with present-semaphore re-chaining) as vk_hook.

The loader/layer link structs (VkLayer*CreateInfo, VkNegotiateLayerInterface)
aren't in Vulkan-Headers, so they're hand-declared to interface version 2. Key
gotcha found via tracing: the loader tags those link structs with small internal
sType values (LOADER_INSTANCE_CREATE_INFO=47, _DEVICE=48), not the 1000000000
range -- matching the wrong value made the device-chain walk fail.

Scoping: an implicit layer loads into every Vulkan app, so it only *captures*
when COOP_VK_LAYER_FORCE is set (tests) or this process's image matches
%TEMP%\coop_vk_target.txt (the host writes it); otherwise pure pass-through.
mock_game_test registers it via VK_LAYER_PATH/VK_INSTANCE_LAYERS and decodes
frames through it. Ships at the bin root with its JSON manifest.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CMakeLists.txt

@@ -131,6 +131,7 @@ if(COOP_BUILD_HOOK)
 	set(SAFETYHOOK_BUILD_DOCS OFF CACHE BOOL "" FORCE)
 	add_subdirectory(third_party/safetyhook)
 	add_subdirectory(hook)
+	add_subdirectory(vk_layer) # coop_vk_layer: implicit Vulkan capture layer (early-presence path)
 	enable_testing()
 	add_subdirectory(tools/audio_tone)  # coop_tone: audio source for the loopback test
 	add_subdirectory(tools/mock_game)   # coop_mock_game: A/V test game for the capture/hook tests