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.toml

@@ -0,0 +1,21 @@
+[package]
+name = "cumulus"
+version = "0.1.0"
+edition = "2024"
+# The version cumulus is built and tested with (pinned in rust-toolchain.toml).
+rust-version = "1.90"
+description = "Brainstorm in the terminal: idea graphs on a 2D canvas, with vim keys and the mouse."
+publish = false
+
+[lints.rust]
+unsafe_code = "forbid"
+
+[lints.clippy]
+all = { level = "warn", priority = -1 }
+
+[profile.release]
+# A smaller, faster program: optimize across all crates at once (lto, in one
+# piece with codegen-units = 1), and leave out the debug symbols (strip).
+lto = true
+codegen-units = 1
+strip = true