`axe: output: document`: report never updates after page state changes

Description

The interactive axe overlay (axe: output: document) is Quarto's tool for an author eyeballing accessibility while editing under quarto preview. It runs axe-core exactly once, at page load. But axe-core evaluates the rendered, visible DOM: color-contrast is computed from the colours on screen right now, and hidden elements (display: none) are skipped entirely. So three ordinary reader interactions invalidate the report, and the overlay gives no indication it's showing results for a state the page is no longer in:

1. Toggling dark/light mode. With theme: {light: ..., dark: ...}, the initial scan runs in whichever scheme loads first. Toggle the scheme and every color-contrast result is potentially wrong. A full page reload re-scans in the persisted scheme, but nothing tells the author a reload is needed.
2. Expanding collapsed content. Violations inside collapsed callouts, folded code, closed tabsets, etc. are invisible to the load-time scan. This case is worse than stale: expanding doesn't trigger a rescan, and a reload re-collapses the content — so these violations are unreachable by the overlay no matter what the author does.
3. Changing window size. Many of our components collapse on small viewports. A user may simulate this by resizing their browser window, but has to reload the page to refresh the scan.

Dashboards already solve this: setupDashboardRescan re-runs axe and rebuilds the report on shown.bs.tab, popstate, and bslib.sidebar — but it's gated to body.quarto-dashboard:

• rescan machinery: https://github.com/quarto-dev/quarto-cli/blob/38ef483b0f01ca91116f51f7e7f1783862be8822/src/resources/formats/html/axe/axe-check.js#L331-L344
• dashboard-only gate: https://github.com/quarto-dev/quarto-cli/blob/38ef483b0f01ca91116f51f7e7f1783862be8822/src/resources/formats/html/axe/axe-check.js#L397-L400

Proposal: extend the same rescan to regular HTML documents when output: document:

• rescan when the colour scheme toggles (the .quarto-color-scheme-toggle click handler / toggleColorMode);
• rescan on Bootstrap state events, as dashboards do: shown.bs.collapse / hidden.bs.collapse (callouts, code folding), shown.bs.tab (tabsets), plus shown.bs.dropdown / shown.bs.modal / shown.bs.offcanvas where relevant;
• and/or a manual "Rescan" button in the overlay as the catch-all, so the author can always refresh the report to match whatever state they've put the page in.

Most of the machinery exists; the work is ungating it and pointing the re-render at the overlay report element rather than the dashboard offcanvas.

This is deliberately scoped to the interactive overlay under quarto preview. Automated coverage of viewport/theme/interaction states (for output: json, CI, etc.) is a different problem I'll write up separately.

Steps to reproduce

---
title: "Axe overlay staleness repro"
format:
  html:
    theme:
      light: flatly
      dark: darkly
    axe:
      output: document
---

## Dark-mode-only contrast failure

<p style="color: #555555;">This paragraph is `#555555` — fine on flatly's white
background, but low contrast on darkly's dark background.</p>

## Collapsed callout hiding a violation

::: {.callout-note collapse="true" title="Expand me"}
<img src="figure.png" width="50" height="50">

The image above has no alt text — invisible to axe while collapsed.
:::

(figure.png is any image; it exists only to carry a missing alt.)

1. quarto preview the document (the overlay needs http:; module scripts don't load from file:).
2. Note the overlay report at the bottom of the page.
3. Click the dark-mode toggle (top right). The page turns dark; the overlay doesn't change.
4. Expand the callout. The overlay doesn't change.

Actual behavior

The overlay shows the load-time scan forever. Verified by driving headless Chrome over CDP and comparing the overlay's contents against a fresh in-page axe.run() after each interaction (Quarto 1.10.12):

Reloading the page in dark mode (the scheme persists via localStorage) does surface the color-contrast violations — confirming they're real and that a fresh scan catches them — but the callout re-collapses on reload, so the image-alt violation can never appear in the overlay.

Expected behavior

The overlay report reflects the page state the author is looking at: it rescans (automatically on scheme toggle and expand/collapse events, or at minimum via a manual "Rescan" button) so that mode-specific contrast failures and violations inside collapsible content are catchable during interactive checking, the way they already are in dashboards.

Your environment

• Quarto 1.10.12
• macOS 26.5.1 (build 25F80), Chrome (headless, CDP) for verification

AI-assisted investigation, grounded in the rendered output and the quarto-cli source at commit 38ef483 (per CONTRIBUTING.md "Using AI tools to investigate").