Fix duplicate schema definitions causing YAML validation issues

[jdonaldson]

Summary

Fixes #14122.

When the same option name (e.g., logo, subject) is defined in multiple schema YAML files, objectRefSchemaFromGlob() silently overwrites — last writer wins. This causes YAML validation errors when users specify valid values that match a "losing" schema variant.

• logo: Add enum: [false] to logo-light-dark-specifier-path-optional so logo: false validates for all formats (dashboard, revealjs, typst), matching the existing logo-light-dark-specifier behavior
• subject: Consolidate into document-metadata.yml as anyOf: [string, object] covering both simple (pdf/office) and structured (epub) forms; remove duplicate entry from document-epub.yml
• Regenerated all build artifacts (json-schemas.json, schema-types.ts, editor tooling)
• Added unit tests for both cases

Test plan

• schema-schema.test.ts — 3/3 pass (schema YAML files well-formed)
• schema-files.test.ts — 4/4 pass (2 existing + 2 new test cases)
  • logo-false.yml — validates false accepted by logo-light-dark-specifier-path-optional
  • subject-structured.yml — validates structured object form passes schema validation
• Manual verification: logo: false in dashboard format renders without validation error
• Manual verification: structured subject in epub format renders without validation error

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[jdonaldson]

Just adding a small comment that there's a human behind this PR. I used Claude here to make some small changes, which were reviewed before submitting. Tests are also added.

[gordonwoodhull]

This pointed out a minor (possibly harmless) bug in resolveLogo so I've added a fix.

[gordonwoodhull]

I've reviewed the logo part (my bug) - looks good, adding a tiny fix.

The subject resolution also makes sense to me.

Claude did not think the structured epub subject test was a rigorous enough test, so we've also added a smoke-all test. I'll let it comment on that.

[gordonwoodhull]

End-to-end epub test for structured subject — The subject-structured.yml schema test inlines a copy of the schema rather than referencing it (unlike the logo-false.yml test which uses ref:). This means it validates the shape of the anyOf but not the actual schema Quarto uses — if someone later changes document-metadata.yml, this test would still pass against its own detached copy. Added subject-structured-epub.qmd as a smoke-all test that renders an actual epub with structured subject metadata and verifies the OPF output contains the expected dc:subject, authority, and term elements. This exercises the full pipeline: schema validation → metadata resolution → Pandoc rendering.

[cscheid]

Hello, and thanks for the PR! We will need you to fill out the original template for the PR, specifically because we need you to attest you've signed the CLA for this project.

[jdonaldson]

Thanks for the review and the additional smoke test, @gordonwoodhull — appreciated.

@cscheid — I took a look at the individual CLA and it's more than I'm comfortable with for a bug fix. Full copyright assignment, blanket patent non-assertion across all Posit software, and open-ended obligations (clause 5) are a significant ask for an external contributor. A DCO or license-grant CLA would be more proportionate, but I understand if that's not on the table.

I'm going to withdraw this PR. The fix is straightforward and well-documented in #14122, so hopefully it's easy for someone on the team to pick up. Wishing you all well — Quarto is a great project.