List inherited methods and module relationships

[samuel-williams-shopify]

Summary

• show superclass, included, prepended, and extended relationships on reference pages
• list inherited documented public and protected methods as links grouped by their defining class or module
• follow Ruby method lookup order while omitting overridden methods, private methods, and constructors
• support instance methods, direct class methods, singleton-class methods, and methods supplied through extend
• require Decode 0.30 for correct lexical resolution of mixin references

This addresses the remaining Utopia Project scope of #12. Metadata extraction remains Decode’s responsibility; the required mixin-reference fix was released in Decode 0.30.0.

Verification

• bundle exec bake test (19 tests, 42 assertions)
• bundle exec rubocop (50 files, no offenses)
• bundle exec bake decode:index:coverage lib (94/94 public definitions)
• inspected generated relationship and inherited-method markup for ReleasesDocument and Guides