fix(mapper): harden Kotlin Gradle role mapping

[steipete]

Follow-up to #38. Hardens Kotlin/Gradle semantic role mapping after maintainer review.

Changes:

• scopes Kotlin project indexes to the owning Gradle root, including nested settings roots
• tightens Android Gradle plugin detection across catalogs, aliases, apply-false forms, strings, comments, and nested blocks
• improves Kotlin role parsing for local types, annotations, supertypes, constructors, wildcard imports, and default/builtin types
• adds mapper regression coverage for the reviewed edge cases
• updates the 0.2.1 changelog with contributor credit

Proof:

• pnpm test src/mapper.test.ts
• pnpm test
• pnpm typecheck
• pnpm lint
• pnpm format:check
• pnpm build
• codex-review --mode branch --parallel-tests "pnpm test src/mapper.test.ts" clean