[ETS] Preserve type-only export metadata

[CaelmBleidd]

Summary

• preserve TypeScript type-only export identity in the native frontend DTO
• expose isTypeOnly through Kotlin ExportInfoDto conversion and public EtsExportInfo
• keep older serialized DTOs and Kotlin call sites compatible with a false default
• cover type-only named, aliased, and star re-exports independently of their runtime declaration kind

Consumer

• required by [TS PBT] Map property coverage to EtsIR usvm#381
• exact consumer pin: aa319129f8b634d3bc1b6b85376a22f06e8739b9

Verification

• frontend npm test: 13 files, 213 tests passed
• ./gradlew --no-daemon :jacodb-ets:test --tests org.jacodb.ets.test.EtsExportTest.testExportInfoTypeOnlyMetadata
• git diff --check origin/neo...HEAD
• GitHub CI: all 8 checks green

The complete local :jacodb-ets:test run in this checkout is blocked by pre-existing missing samples/etsir/ast JSON fixtures; the full frontend suite, focused Kotlin contract test, and remote ETS/core/lifecycle suites pass.

[github-actions]

Test Results

  225 files  ±0    225 suites  ±0   15m 18s ⏱️ - 1m 4s
  777 tests +1    765 ✅ +1  12 💤 ±0  0 ❌ ±0 
2 047 runs  +1  1 997 ✅ +1  50 💤 ±0  0 ❌ ±0 

Results for commit aa31912. ± Comparison against base commit 9ea3387.