Rename framework namespace to Shift

[rtcoder]

Summary

• Rename the framework public namespace from Engine\ to Shift\ across the core, example module, tests, bootstrap, and documentation.
• Map Composer PSR-4 autoloading from Shift\ to the existing Engine/ core directory.
• Remove stale Tools\ and Console\ Composer autoload roots now covered by Shift\.
• Add a middleware pipeline with class-based and callable middleware support.
• Allow middleware to wrap controller dispatch, modify responses, or short-circuit requests.
• Mark completed roadmap items and next refactoring steps in REFACTORING.md.

Validation

• composer validate --strict --no-check-publish
• composer dump-autoload
• find Engine application tests -name '*.php' -print0 | xargs -0 -n1 php -l
• composer test
• php shift.php route:list
• php shift.php health
• HTTP smoke tests:
  • GET /health -> 200 application/json
  • GET /hello -> 404 application/json

Release

• Version label: v0.9.0