feat(rembg): add RemoveBG Studio - native background removal app

C++ WebView2 host app driving a Python/rembg engine as a JSON-stdio
sidecar, with live before/after preview for images and video frames.
Also includes the original CLI (removebg.py) built on the same
core/ engine.

The WebView2 SDK is fetched on demand via
native/third_party/fetch-webview2.ps1 (wired into the Makefile)
rather than vendored, since it's ~15MB of prebuilt/generated
Microsoft SDK content. A Makefile provides make sync/build/run/clean
as the standard entry points.

README.md

@@ -22,6 +22,10 @@ sudo python3 fake-wheel/fake_wheel_uinput.py
 
 Requires Linux with the `uinput` kernel module and either root access or a user in the `input` group.
 
+### [RemoveBG Studio](./rembg/)
+
+AI background removal for images and video, with lossless FFmpeg frame extraction/reassembly. Ships as a native Windows app (C++ host embedding WebView2, driving a Python/rembg sidecar over JSON-stdio) with a live before/after preview, plus a scriptable CLI and a legacy Tkinter GUI fallback. See [rembg/README.md](./rembg/README.md) for build/usage details.
+
 ### [VidBoard Setup](./vidboard-setup-rs/)
 
 A Rust TUI installer that copies VidBoard AI model files into existing ComfyUI and Ollama installations on Windows. Automatically detects both applications via open ports, running process command lines, environment variables, and known install locations — pre-filling the paths so you only need to confirm and press Enter.