Add vlibc scaffold, build system, and documentation

Establish the repository layout per Vox guidelines (layouts/C.md,
building/C.md): Autotools build (GCC-only, C23), five compatibility
profiles (--enable-onlyposix/--enable-muslmimic/--enable-muslext/
--enable-spoof, default vlibc), alongside/overwrite install methods,
vlibc-gcc/vlibc-clang drivers, static-linking requirement (except
spoof), benchmark harness, and tooling (.clang-format/.clang-tidy/
.clangd + compile_commands.json).

README.md

@@ -1,3 +1,72 @@
 # vlibc
 
-A modern replacement for glibc, with modern features and extensions of the standard. Plus compatibility with glibc.
+A modern replacement for glibc: a performant, standard-conforming C library
+with modern extensions and high glibc compatibility.
+
+vlibc is written in C (C23, with C2y/C29 opt-in), built with Autotools and a
+single compiler (GCC, no fallback). Full static linking is a first-class,
+required capability.
+
+## Capabilities
+
+- **Five compatibility profiles**, from the lightest to the most compatible:
+  1. `--enable-onlyposix` — pure POSIX, nothing more.
+  2. `--enable-muslmimic` — musl-like, light and musl-compatible.
+  3. `--enable-muslext` — musl-extended.
+  4. `--enable-spoof` — a glibc replica, for drop-in compatibility with
+     scripts and programs that rely on long-standing glibc behavior.
+  5. *(default)* — **vlibc**: glibc-extended, without the spoofing layer, but
+     with extended standard features and high glibc compatibility.
+- **Two install methods** (`--with-install=`):
+  - `alongside` (default) — install next to the system libc, under a
+    vlibc-specific tree; the system libc is left untouched.
+  - `overwrite` — replace the system libc in place.
+- **`vlibc-gcc` and `vlibc-clang`** compiler drivers, so consuming projects
+  build against vlibc with either compiler.
+- **Full static linking** is required for every profile except `spoof`.
+- **Compiler intent** is declared on the public API (e.g.
+  `__attribute__((const))`) so the compiler can fold and eliminate calls,
+  keeping statically linked binaries small.
+
+## Build
+
+```sh
+./autogen.sh                 # regenerate build system + configure
+make                          # build
+make debug                    # build with -O0 -g3 into bin/debug/
+make release                  # build with -O3 into bin/release/
+make bench                    # build and run benchmarks
+make clean                    # remove build artifacts
+make compile-commands         # regenerate compile_commands.json (needs bear)
+```
+
+Common configure options:
+
+```sh
+./autogen.sh --enable-spoof                     # glibc replica profile
+./autogen.sh --with-install=overwrite           # replace system libc
+./autogen.sh --with-libc=glibc                  # benchmark against glibc
+./autogen.sh --enable-c29                       # experimental C2y (C29)
+```
+
+User-provided `CFLAGS` and `LDFLAGS` are honored.
+
+## Layout
+
+```
+include/        public headers (mandatory)
+src/            implementation sources
+benchmarks/     benchmark harnesses (vs. glibc/musl)
+docs/           behavior and glibc-difference documentation
+thirdparty/     vendored third-party libraries
+tools/          vlibc-gcc / vlibc-clang driver templates
+bin/{release,debug}/  build outputs
+```
+
+## Documentation
+
+- `docs/overview.md` — what vlibc is and how it behaves.
+- `docs/compatibility.md` — the five profiles and glibc differences.
+- `docs/install.md` — the two install methods.
+- `CONTRIBUTING.md` — how to contribute.
+- `STYLEGUIDE.md` — how code should look.