Add an Open in Claude split button to the page actions

[enf0rc3]

Adds an Open in Claude split button to the page actions row, between Copy as markdown and Edit on GitHub, per the Figma ordering.

Implements the Open in LLM design, using the SplitButton component from #3340.

Replaces #3330, which carried stack metadata from when it was based on wl/split-button. Same branch, same commit, no content change.

The primary half opens Claude with a prompt pointing at the page's .md URL. The caret opens a menu with Open in Claude and Open in ChatGPT, as link-styled rows with a provider logo and an external-link icon. The prompt carries an absolute URL, because the assistant fetches the page itself rather than following a link from this site.

Gemini is deliberately absent: gemini.google.com ignores prompt parameters, so the entry could only prefill by pointing at AI Studio, which is not where "Open in Gemini" says it is going.

Four files, additions only — the component, its strings, one line in the layout, and its tests. The icons and getPageMarkdownPath() both come from what has already landed.

Carried over from #3330: the per-component icon masks here would be better as a global icons.css, deliberately left for a follow-up.

Testing

Clean astro build, 2674 pages, 1253 .md emitted. 36 passed across open-in-llm, split-button, copy-button and llm-endpoints. Playwright is not wired into CI, so that is a local run.

The positioning tests wait for the menu's open animation to settle, the same way split-button.spec.ts does — measured mid-animation the icon box reads 12x9 rather than the 16x16 it lands on.

Measured where the menu ends up, to confirm those tests hold something down:

viewport	menu	opens towards
1200	641–834	start edge
700	321–514	start edge
430	159–353	flips to the end edge

430 is where the row wraps and the fallback fires, which is the case split-button.spec.ts could not reach on its own: the component gallery gives the control room on both sides at every width.

🤖 Generated with Claude Code

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[rosslovas]

Looks good! In the design it looks like the full non-compact menu, I'm assuming you've chosen to go with compact deliberately