Fix revealjs and epub callout id rendered on two divs

[cderv]

In revealjs and EPUB output, a callout with an id renders that id on two nested divs:

<div id="my-id" title="Titled">
<div id="my-id" class="callout callout-note callout-titled callout-style-default">

Duplicate ids are invalid HTML. getElementById() returns only the outer div, and a CSS #my-id rule applies to both (doubled borders, margins, padding). HTML output is not affected: the bootstrap renderer emits a single .callout div.

Root cause

The revealjs/epub renderer wraps the .callout div in an outer div so leftover classes such as .fragment survive (#5208, #6853). The wrapper was created whenever the callout had an id, and it received the full attribute set, identifier included. When cross-referenceable callouts were added (a0a7b4a, first released in v1.4.458), the inner .callout div started carrying the id as well, so both divs have it. Reproduced on released 1.4.549 and v1.9.38, and on current main.

Fix

The id stays on the .callout div, the same element as in HTML output, so .callout#x selectors behave the same across formats. The wrapper is now created only when classes or attributes are left over, and it gets a copy of the attributes without the identifier. An id-only callout renders as a single div.

Alternative considered: keeping the id on the wrapper and blanking the inner one. This was rejected because the id would no longer be on the .callout element, and .callout#x (used in the existing revealjs-callouts.spec.ts locators) would stop matching.

This changes what #x selects in revealjs and EPUB, so it targets 1.11 without a backport. Selectors such as #x > .callout or getElementById('x').querySelector('.callout') no longer match, and neither works in HTML. Reveal fragment-event code keyed on event.fragment.id for {#x .callout-note .fragment} is affected too, since .fragment stays on the wrapper.

The title attribute still leaks onto the wrapper as an HTML attribute, which keeps titled callouts wrapped. That is separate from this fix.

Test plan

• div.callout#… selectors and absence of [id=x] [id=x] in the new smoke-all document, reverse-applying the fix gives an assertion failure
• 6853.qmd (fragment wrapper) still passes
• EPUB: unzip the rendered .epub and grep -rhn 'id="my-id\|id="other' EPUB/text/ shows one line per id, each on class="callout …"

Fixes #15036

Checklist

I have (if applicable):

• referenced the GitHub issue this PR closes
• updated the appropriate changelog in the PR
• ensured the present test suite passes
• added new tests
• created a separate documentation PR in Quarto's website repo and linked it to this PR

AI-assisted PR

• AI tool used: Claude Code
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