Summary

• Adds the tsconfigPathsPlugin transformer to the afterDeclarations phase in both compiler.ts and watch-compiler.ts
• Previously, path aliases (e.g., @core/*) were only resolved in .js output but left unresolved in .d.ts files
• This caused broken type resolution when the build output was consumed as a library

The fix is minimal — just 3 lines of production code, reusing the existing transformer.

Closes #1749

Test plan

• Added 2 new tests verifying path aliases are resolved in .d.ts output
• Added test fixtures with aliased imports
• All 153 tests pass (21 suites)
• Manual test: nest build with path aliases produces .d.ts files with relative imports