Add a pass-through renderer plugin

t5deRenderEngine.dll implements IMVU Classic's renderer plugin interface by wrapping IMVU's own OpenGL renderer, and logs what each frame calls, to prove our declarations of the interface. Built with CMake presets for 32-bit MSVC; docs/interface.md has the findings.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

README.md

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+# t5de-renderer
+
+A new 3D renderer for the IMVU Classic client, as a renderer plugin the client loads like its own OpenGL renderer.
+Part of [T5DE](https://git.t5de.dev/t5de/t5de); unofficial, not affiliated with IMVU.
+
+For now it's a pass-through: it wraps IMVU's OpenGL renderer and logs what each frame draws, to prove our
+declarations of IMVU's interface (`docs/interface.md`).
+
+## Building
+
+Needs Visual Studio Build Tools 2026 (the C++ workload) and CMake 3.28 or newer. IMVU Classic is a 32-bit
+Visual C++ program, so the plugin is built for 32-bit Windows (the `windows-x86` preset):
+
+```sh
+cmake --workflow --preset release
+```
+
+That configures, builds `build/windows-x86/Release/t5deRenderEngine.dll` and runs the tests. Or step by step:
+`cmake --preset windows-x86`, `cmake --build --preset debug`, `ctest --preset debug`.
+
+## Trying it
+
+Copy `t5deRenderEngine.dll` into a T5DE client folder, and have the client load it in place of
+`glRenderEngine.dll` (a T5DE patch, to come), then choose OpenGL in Settings > Advanced. The log is
+`%TEMP%\t5de-renderer.log`.