docs: remove Arabica network references

[jcstein]

Summary

• remove the Arabica network page, navigation entry, image, version constants, and release-sync support
• remove Arabica tabs, endpoints, faucets, upgrade history, and availability guidance across operator and developer docs
• update docs generation, link checking, endpoint checking, and contributor guidance to cover Mainnet Beta and Mocha only

Why

Arabica is being sunset and its replacement testnet is internal-only, so public documentation should no longer direct users to Arabica or expose the replacement network.

Impact

The public site now presents Mainnet Beta and Mocha as the supported public networks. The deleted Arabica route is no longer generated, and rendered/searchable docs contain no Arabica references.

Validation

• yarn lint (passes with one pre-existing warning in NodeAPIContent.tsx)
• yarn build
• rendered HTML/Markdown scan for Arabica references and deleted-route links
• git diff --check
• latest-tags mainnet filtering assertions
• CI preview deployment and CodeQL
• CI link scan: 0 broken internal links

Notes

• Local yarn check-links cannot start under Node 26 because glob imports a GLOBSTAR export that the pinned minimatch version does not provide.
• CI's link-check failure is unrelated to this diff: three external URLs already fail on main (two Etherscan 403 responses and one retired zkSync staging explorer), plus an unchanged Mainnet provider returned a transient 502.
• Historical versioned OpenRPC snapshots under public/specs/ are intentionally unchanged because they are upstream release artifacts and are not rendered or indexed as authored docs.

Linear: https://linear.app/celestia/issue/PROTOCO-2210/remove-all-references-of-arabica-from-celestia-app-docs-website

[github-actions]

🚀 Preview Deployment

Your preview is ready: https://celestiaorg.github.io/docs-preview/pr-2547/

[rach-id]

all is good except for one nit