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.

rembg/pyproject.toml

@@ -0,0 +1,30 @@
+[build-system]
+requires = ["setuptools>=61.0"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "removebg-studio"
+version = "0.1.0"
+description = "AI Background Removal for Images and Videos powered by rembg & FFmpeg"
+readme = "README.md"
+requires-python = ">=3.10"
+dependencies = [
+    "rembg>=2.0.50",
+    "pillow>=10.0.0",
+    "tqdm>=4.65.0",
+    "onnxruntime>=1.15.0",
+    "numba>=0.60.0",
+]
+
+[project.scripts]
+removebg = "removebg:main"
+
+[tool.setuptools.packages.find]
+where = ["."]
+include = ["core*"]
+
+[tool.setuptools]
+py-modules = ["removebg"]
+
+[tool.uv]
+package = true