Add the project skeleton and the approved design

Cargo.toml with the release profile and lints, the toolchain pinned to
Rust 1.90.0, a build script that records the git commit for
`cumulus --version`, and rustfmt settings and cargo aliases (`cargo lint`,
`cargo linux`) as in skyshift. DESIGN.md holds the design approved after
the question rounds; README.md has build instructions and the planned keys.

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

.cargo/config.toml

@@ -0,0 +1,15 @@
+# Windows (MSVC): link the C runtime statically, so cumulus.exe runs on any
+# Windows 10/11 machine without installing the "Visual C++ Redistributable".
+[target.'cfg(all(windows, target_env = "msvc"))']
+rustflags = ["-C", "target-feature=+crt-static"]
+
+[alias]
+# `cargo lint`: the strict check to run before committing.
+lint = "clippy --all-targets -- -D warnings"
+# `cargo linux`: build a Linux binary from any OS. It's fully static, so the
+# same file runs on Void (glibc or musl), Fedora and other distributions:
+# target/x86_64-unknown-linux-musl/release/cumulus
+linux = [
+    "build", "--release", "--target", "x86_64-unknown-linux-musl",
+    "--config", "target.x86_64-unknown-linux-musl.linker = 'rust-lld'",
+]