Fix preview modulemap and module resolution

[k-kohey]

Summary

• Include third-party dependency manifest module maps even when they live outside the build
  directory, while still skipping SDK/toolchain module maps.
• Parse header directives in non-framework module maps to derive include paths.
• Resolve preview thunk module names from Index Store data and tolerate macOS /tmp and /private/
  tmp path aliases.

Verification

• go test ./internal/preview/build -count=1
• go test ./internal/preview/analysis -run 'TestIndexStoreCache|
  TestBuildTransitiveDeps_WithCache' -count=1
• go test ./internal/preview -run 'TestModuleNameForSource|TestParseTrackedFiles|
  TestCompilePipeline|TestGenerate' -count=1
• Built local axe binary and generated Preview report successfully for 3 files / 8 previews