feat(docs): add theme parity, anchors, search, and Steps

[Akanimoh12]

Summary

• Add pre-paint light/dark theme resolution with a persistent docs preference and theme toggle.
• Generate stable heading IDs and copyable heading permalink affordances, while honoring explicit {#id} anchors.
• Add a Pagefind-backed documentation search dialog using the generated static search index.
• Render numbered <Steps> procedure blocks with visible connectors.

Verification

The repository validation gate was skipped at the user's request before publication. The change was committed and pushed from feat/docs-dx-038-039-042-044.

Issues

Closes #551
Closes #556
Closes #554
Closes #550

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