Rename CLI entrypoint to shift

[rtcoder]

Summary

• rename the CLI entrypoint from shift.php to executable shift
• switch the shebang to /usr/bin/env php and load bootstrap.php relative to the entrypoint
• update command help text, generated command stubs, README, developer docs, tests, and CI examples to use ./shift
• lint the extensionless CLI entrypoint in the API workflow

Tests

• composer validate --no-check-publish
• php -l shift
• find src application tests -name '*.php' -print0 | xargs -0 -n1 php -l
• composer test
• ./shift route:list
• ./shift health