Add module discovery cache

[rtcoder]

Summary

• add module discovery cache support in ModuleLoader
• add cache:modules, cache:status, and cache:clear CLI commands
• store generated module cache under storage/cache/modules.php and ignore runtime cache files
• document production cache usage in README, developer docs, and refactoring notes

Tests

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