build(website): update astro and @astrojs/markdown-remark to satisfy Starlight 0.42 peers

[dangreen]

Summary

The Website deploy has been failing since #192. Starlight 0.42 brings @astrojs/mdx@8, whose peers are @astrojs/markdown-remark@^7.3.0 and astro@^7.2.10, while the lockfile kept @astrojs/markdown-remark@7.2.1 and astro@7.0.6: the website's ^ ranges allowed the newer versions, but nothing asked for them, so astro build fails with:

`@astrojs/markdown-remark` is too old to render `.mdx` files. Update it to the latest version — a `^` range on an older version will not pick it up

This bumps the website's ranges to @astrojs/markdown-remark@^7.3.0 and astro@^7.3.1, so the lockfile resolves 7.3.0 and 7.3.1.

Test plan

• pnpm docs:build locally: astro check 0 errors, 22 pages built
• Website workflow on main after merge

🤖 Generated with Claude Code

[coveralls]

Coverage Report for CI Build 33973336855

Coverage remained the same at 69.769%

Details

• Coverage remained the same as the base build.
• Patch coverage: No coverable lines changed in this PR.
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	1046
Covered Lines:	725
Line Coverage:	69.31%
Relevant Branches:	211
Covered Branches:	152
Branch Coverage:	72.04%
Branches in Coverage %:	Yes
Coverage Strength:	11.05 hits per line

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💛 - Coveralls