feat(render): dynamic OpenGL/Vulkan backend split and backend-neutral viewer

- Extract libolive-rendercore static library to minimize backend link boundary.
- Add DynamicRenderer adapter with C ABI (oakgl/oakvulkan shared libs).
- Make OAK_ENABLE_DYNAMIC_RENDER_BACKEND default ON with OpenGL fallback.
- Implement VulkanRenderer prototype (textures, shaders, UBO blit, readback).
- Add backend-neutral viewer readback path (offscreen -> QImage -> QPainter).
- Refactor PluginRenderer to be renderer-agnostic; OFX plugins fall back to CPU
  path on non-OpenGL backends while preserving OpenGL render path.
- Add Renderer::AttachOutputTexture/DetachOutputTexture and C ABI forwards.
- Update docs/zh/render-backend-dynamic-plan.md for Phase 3/4/5.

app/common/ffmpegutils.h

@@ -30,6 +30,7 @@ extern "C" {
 
 #include <olive/core/core.h>
 
+#include "common/avframeptr.h"
 #include "render/videoparams.h"
 
 namespace olive
@@ -85,16 +86,6 @@ public:
 	static AVPixelFormat ConvertJPEGSpaceToRegularSpace(AVPixelFormat f);
 };
 
-using AVFramePtr = std::shared_ptr<AVFrame>;
-inline AVFramePtr CreateAVFramePtr(AVFrame *f)
-{
- 	return std::shared_ptr<AVFrame>(f, [](AVFrame *g) { av_frame_free(&g); });
-}
-inline AVFramePtr CreateAVFramePtr()
-{
-	return CreateAVFramePtr(av_frame_alloc());
-}
-
 }
 
 #endif // FFMPEGABSTRACTION_H