[codex] Prevent indexing development builds

[cormoran]

Description

Development and preview builds now emit a robots meta tag with noindex, nofollow by default so search engines do not index them.

The release workflow explicitly sets VITE_ROBOTS to index, follow, preserving indexing for the production release build.

CLA (Contributor License Agreement)

By submitting this pull request, I agree that my contributions
are licensed under the project's current license.

I also grant the maintainer(s) of this project the right to relicense
my contributions under any license, for use in future versions of the project.
This does not affect the license of any previously released versions.

Validation

• npm run lint
• npm test
• npm run build
• env VITE_ROBOTS='index, follow' npm run build
• Confirmed dist/index.html contains noindex, nofollow by default and index, follow when VITE_ROBOTS is set.

[github-actions]

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_{Deployed from commit f919457}