Fix default HTML bundled template resolution

[oscarcv]

Summary

• Fix default HTML template lookup so snapshot-report can always render HTML without requiring --html-template.
• Prefer loading the bundled template via Bundle.module first.
• Expand filesystem fallback candidates to support both bundle layouts used in packaging:
  • SnapshotReportKit_SnapshotReportCore.bundle/default-report.stencil
  • SnapshotReportKit_SnapshotReportCore.bundle/Contents/Resources/default-report.stencil
• Update template-candidate tests to assert both bundle layouts.

Checklist

• I ran swift test
• I updated docs if behavior changed
• I added/updated tests for new behavior
• I verified CI-related files if workflow behavior changed

Validation

• Commands run:
  • swift test --filter htmlRendererTemplateCandidatesIncludeResolvedSymlinkPath
  • swift test --filter htmlRendererTemplateCandidatesIncludeSourceFallback
  • swift test

Screenshots / Artifacts (if applicable)

• N/A