fix(create-project): align with Composer's CreateProjectCommand pipeline

Split the inline 370-line execute() into execute / install_project /
install_root_package, mirroring Composer's three-method shape and argument
order. Replace the bespoke caret/tilde/wildcard semver helpers with
mozart_semver::VersionConstraint, harden stability inference (handle the
@stability suffix and reject invalid values), and align user-facing wording
("Creating a ...", "Cannot create project directory ...", "Could not find
package ...") with Composer's strings. Add the --ask directory prompt, the
interactive VCS-removal prompt, the empty-target-directory bail, and the
COMPOSER_ROOT_VERSION / COMPOSER env-var handling that the PHP command does
after extraction.

Custom repositories, the canonical Installer pathway, the signal handler,
and script events are still deferred — see .ken/command_compat_plan/create_project.md.

0 files changed, 0 insertions, 0 deletions