refactor: align builders with feature aliases

[wellwind]

Summary

• switch the custom builders to import shared Markdown helpers via the new @features and @shared/core aliases
• configure the builders TypeScript config and build pipeline to resolve those aliases and rewrite the emitted requires
• add an alias post-processing script that also cleans up stray compiled JS left in the source tree after a build

Testing

• npm run build:builders
• npm test

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https://chatgpt.com/codex/tasks/task_e_68cce694f3208321a1394b4cc831bc9f

[wellwind]

LGTM