Add CLI diagnostic commands

[rtcoder]

Summary

• add ./shift test for running the project test suite through the framework CLI
• add ./shift about with framework, PHP, environment, and path information
• add ./shift env:check for validating required environment variables
• add ./shift db:check for checking configured PDO database connectivity
• add ./shift module:list for listing discovered modules, config status, and command mappings
• document the new commands in README and developer docs

Tests

• composer validate --no-check-publish
• php -l shift
• find src application tests -name '*.php' -print0 | xargs -0 -n1 php -l
• composer test
• ./shift test
• ./shift about
• ./shift module:list
• APP_ENV=testing DB_CONNECTION=sqlite DB_DATABASE=:memory: ./shift env:check
• DB_CONNECTION=sqlite DB_DATABASE=:memory: ./shift db:check
• ./shift route:list
• ./shift health