Add OpenGL capture path for the hooked video mirror

The Present hook never fired in Phantom Brave because it's an OpenGL game
(OPENGL32.dll loaded, IDXGISwapChain::Present calls=0), so the hooked video source
showed no image. Add an OpenGL producer under the video subsystem: inline-hook
gdi32!SwapBuffers + opengl32!wglSwapBuffers (with a re-entrancy guard, since
SwapBuffers calls wglSwapBuffers), glReadPixels the backbuffer, flip it, and upload
it into the same shared keyed-mutex texture the host already samples -- so the host
is unchanged. DXGI games still hit the Present hook; both producers are installed
and whichever the game uses fills the texture.

Validated by opengl_hook_test (real GL context, clears to a known color, reads the
exact pixels back through the shared texture) and against Phantom Brave (SwapBuffers
~75/s, present=0, shared texture 1920x1080, generation advancing). Vulkan
(vkQueuePresentKHR) still needs WGC -- documented. All 7 tests pass.

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

hook/src/opengl_hook.hpp

@@ -0,0 +1,30 @@
+// Injected OpenGL capture path: hooks SwapBuffers / wglSwapBuffers in OpenGL games
+// (which never call IDXGISwapChain::Present, so the DXGI present hook can't see
+// them -- e.g. Phantom Brave), reads the GL backbuffer with glReadPixels, and
+// uploads it into the same shared keyed-mutex texture (coop_video_<pid>) the host
+// samples. Part of the video subsystem, alongside present_hook.
+//
+// glReadPixels forces a GPU->CPU readback each frame, so this is heavier than the
+// D3D shared-texture copy; fine for the 2D / lower-framerate games that tend to be
+// OpenGL. Vulkan games present via vkQueuePresentKHR and aren't covered here (see
+// the README) -- use WGC for those.
+#pragma once
+
+#include "ipc_client.hpp"
+
+namespace coop::hook
+{
+
+// Installs the OpenGL swap hooks. `ipc` must outlive the hooks. Returns true if at
+// least SwapBuffers was hooked. Safe to call repeatedly.
+bool install_opengl_hooks(IpcClient& ipc);
+
+// Removes the OpenGL swap hooks and releases the shared texture (best effort).
+void remove_opengl_hooks();
+
+// --- Diagnostics -----------------------------------------------------------
+
+std::uint64_t opengl_swaps();         // cumulative SwapBuffers/wglSwapBuffers detours
+std::uint64_t opengl_frames_shared(); // frames uploaded into the shared texture
+
+} // namespace coop::hook