[M1] add cargoxx new

CHANGELOG.md

@@ -36,3 +36,10 @@ All notable changes to cargoxx will be documented in this file.
   sorts results for deterministic output, and returns `LayoutNoTarget`
   when neither a library nor any binary is present.
   `tests/layout_discovery.cpp` covers 12 cases.
+- `cargoxx new <name>` and `cargoxx new --lib <name>` scaffold a project
+  directory with `Cargoxx.toml`, `src/main.cpp` or `src/lib.cppm`, and a
+  minimal `.gitignore`. Hyphens in the package name are mapped to
+  underscores when generating the module/namespace identifier.
+  Codegen of `flake.nix` / `CMakeLists.txt` is intentionally deferred to M3.
+  CLI11 v2.6.2 vendored at `third_party/CLI11.hpp`; entry point is now
+  `cargoxx::cli::run(argc, argv)`. `tests/cmd_new.cpp` covers 9 cases.