Evidence — foldable Obsidian callouts are accessible disclosures (PR #200)

Obsidian callouts with a fold marker — > [!type]+ (expanded) or > [!type]- (collapsed) — render as an accessible disclosure: the title becomes a keyboard-operable <button aria-expanded> with a chevron, and the body shows/hides on activation (click or Enter/Space). Before this change, a - callout's body was permanently hidden with no way to reveal it.

The callout is upgraded from a plain <blockquote> by the client-side resolver (assets/js/obsidian-wiki-links.js), so this evidence is captured in a real browser against the Live example block added to the syntax-reference doc.

How this evidence was produced

../../obsidian-callouts-evidence.mjs loads /docs/obsidian/syntax-reference/, reads the collapsed [!note]- callout's state, activates its title button, and re-reads it.

docker compose up                                                  # serves :4000
BASE_URL=http://localhost:4000 node test/visual/obsidian-callouts-evidence.mjs

What each file shows

• 01-disclosure-before-after.png — the collapsed [!note]- callout before vs after activating its title: the chevron rotates, the body is revealed, and aria-expanded flips false → true.
• 02-expanded-default.png — a [!tip]+ callout renders open by default (aria-expanded="true", body visible).
• metrics.json — the measured aria-expanded / body hidden / data-collapsed values for each state.

Measured transitions (from metrics.json)

Callout	aria-expanded	body hidden	data-collapsed
[!note]- collapsed (initial)	false	true	true
[!note]- after activation	true	false	removed
[!tip]+ (default)	true	false	—

The title is a real <button> in every foldable callout (keyboard operable).

Regression test: ../../obsidian-callouts.spec.js (smoke tier) pins these transitions; the resolver DOM shape is unit-tested in ../../test_resolver.js and the Ruby-plugin parity in ../../test_ruby_converter.rb.