Fix isolated Blume docs rendering

[sarthakagrawal927]

What changed

• Exposes Astro 7.1.3 and the three integrations imported by Blume's generated config as direct development dependencies.
• Reuses the exact versions already resolved transitively by Blume.
• Leaves runtime dependencies and unrelated transitive lock entries unchanged.

Root cause

Blume generates .blume-verify/astro.config.mjs at the repository root. Under pnpm's strict dependency layout, that generated config could not resolve astro/config or its @astrojs/mdx, @astrojs/react, and @shikijs/twoslash imports because they were only available inside Blume's dependency tree.

Impact

The Docs workflow can complete its isolated Blume render instead of failing after link validation.

Validation

• pnpm install --frozen-lockfile --ignore-scripts
• /opt/homebrew/bin/bash ./scripts/check-docs-links.sh
• Fresh ./scripts/docs-validate.sh after moving the previous .blume-verify runtime (18 pages built)
• pnpm build
• Fleet code-cleanup dependency review
• git diff --check

Closes #9