docs: add Spinner, GlobalHeaderLayout and sidebar-layout body-slot pages

[interacsean]

Salvages the usable half of the Documentation Updater's output in #541, which is conflicted against main and cannot be merged as-is.

Why not just rebase #541

It was generated before #515 landed, so 13 of its 23 files conflict. I merged it locally to check what those conflicts actually are: every one is an astw: removal that #515 already did better.

File	#541	main (#515)
layout.md	<Layout className="gap-6">	<Layout gap={6}> — the real prop
layout.md	className="bg-gray-50"	className="bg-muted" — semantic token
alert.md	deleted the explanation	kept it, linked to the styling concept page

Resolving those 13 files by hand would land back exactly where main already is. All 13 are resolved to main, so none of them appear in this PR.

Four more (table, timeline, tooltip, quickstart) drop out entirely — main already carries the same corrections.

What's actually here

Six files, all with no counterpart on main:

• docs/components/spinner.md — new page. Spinner ships in this release with no docs at all. Size table (12/14/16/20) and the decorative-unless-named aria behavior verified against SPINNER_SIZES and the component source.
• docs/components/global-header-layout.md — new page. All four common props and their defaults, the children/body mutual exclusivity, and all six namespaced parts verified against global-header-layout.tsx.
• docs/components/sidebar-layout.md — documents the body slot and topBar. main does not mention body anywhere. fix(core): correct astw: prefix order in shipped components, and the prefix advice in docs/ #515's styling-boundary note was lost in the generated rewrite and is restored here.
• docs/components/default-sidebar.md, command-palette.md, use-page-meta.md — brought in step with the shipped API.

One deletion worth calling out: the palette page's "Custom Palette (Advanced)" section is gone. It demonstrated useCommandPalette and navItemsToRoutes, neither of which is exported from index.ts — the example could never have compiled.

CLAUDE.md is untouched. The generated pass appended a nine-entry ### Documentation Index alongside the convention table from #540 — the enumerated shape that rotted the previous one — so that hunk is dropped.

Why this is worth landing before the release

Merging the Version Packages PR (#524) deletes all 13 changesets, and the Documentation Updater reads .changeset/*.md as its only input, calling noop when there are none. Once you publish, the automation can no longer document this release — anything missing has to be written by hand.

Verification

• pnpm fmt:check — clean, 640 files
• Catalogue link script — 28 pages OK
• All relative links in the six changed files resolve to existing targets
• astw: count across docs/ unchanged from main (10 mentions, all correctly describing it as internal)

Closes #541.

🤖 Generated with Claude Code

[github-actions]

Code Metrics Report

	main (7748583)	#542 (dcb1247)	+/-
Coverage	87.4%	87.4%	0.0%
Test Execution Time	1m56s	1m47s	-9s

Details

  |                     | main (7748583) | #542 (dcb1247) | +/-  |
  |---------------------|----------------|----------------|------|
  | Coverage            |          87.4% |          87.4% | 0.0% |
  |   Files             |            204 |            204 |    0 |
  |   Lines             |           6014 |           6014 |    0 |
  |   Covered           |           5257 |           5257 |    0 |
+ | Test Execution Time |          1m56s |          1m47s |  -9s |

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Reported by octocov