chore: vendor trimmed v4l2r capture crate

libs/v4l2r/README.md

@@ -0,0 +1,24 @@
+# Rust bindings for V4L2
+
+This is a vendored, One-KVM-specific subset of `v4l2r`.
+
+It keeps only the pieces needed for video capture:
+
+- generated Linux V4L2 bindings,
+- safe low-level ioctl wrappers used by capture and device probing,
+- memory handle helpers for `MMAP`, `USERPTR`, and `DMABUF`,
+- core V4L2 types such as `Format`, `PixelFormat`, and `QueueType`.
+
+The upstream crate also contains high-level device abstractions, stateful
+decoder/encoder helpers, stateless codec controls, examples, and C FFI. Those
+parts are intentionally removed here so this dependency stays scoped to capture.
+
+## Build options
+
+`cargo build` generates V4L2 bindings from `/usr/include/linux/videodev2.h` by
+default. Set `V4L2R_VIDEODEV2_H_PATH` to a directory containing `videodev2.h` to
+generate bindings from a different header.
+
+For Android targets, the build script uses the Android NDK sysroot. Set one of
+`ANDROID_NDK_HOME`, `ANDROID_NDK_ROOT`, `NDK_HOME`, `ANDROID_HOME`, or
+`ANDROID_SDK_ROOT` if the NDK cannot be found automatically.