follow-up: restore path aliases with TS 6.x-compatible configuration

[carlos-alm]

Deferred from PR #667 review.

Original reviewer comment: Claude automated review on PR #667 suggested restoring path aliases (#shared/*, #infrastructure/*, #db/*, etc.) using TS 6.x-compatible configuration.

Context: PR #667 removed the baseUrl and paths entries from tsconfig.json because they were deprecated in TypeScript 6.x (TS5101 error). While the aliases were never used in imports (all 849+ imports use relative paths), restoring them with modern TS 6.x configuration and gradually migrating the 300+ relative ../../ imports to path aliases would improve code readability.

What needs to be done:

1. Research the TS 6.x replacement for baseUrl/paths (likely Node.js subpath imports via package.json imports field, or tsconfig.json paths without baseUrl)
2. Configure the aliases in a TS 6.x-compatible way
3. Optionally migrate existing relative imports to use the aliases