fix(scan): show validator 'Registered' timestamp on detail page

[satyakwok]

Summary

Operator noticed scan v1's validators page has no "how long this validator has been online" indicator. The chain's legacy /validators endpoint exposes registered_at (unix seconds) but fetchValidators was only pulling name + blocks_produced from it. This carries registered_at through to the merged row and renders a Registered InfoRow on the detail page under Status.

Field already exists on ValidatorData — no chain-side change needed.

Why detail page only

List page stays clean. Showing "registered" on the detail page is the standard explorer pattern (Etherscan's "Created", Solana Beach's "Started" both live there, not on list rows).

Verification

curl https://rpc.sentrixchain.com/validators | jq '.validators[0]'
# returns: { address, blocks_produced, is_active, name, registered_at: 1777030372 }

After this PR: clicking through to a validator detail page shows e.g. "Registered: Apr 23, 2026" between Status and Stake.

Test plan

• Visit scan.sentrixchain.com/en/validators/0x4cad... and confirm "Registered" row renders
• Visit a testnet validator detail page — same field surfaces
• pnpm --filter=@sentriscloud/scan typecheck green (verified locally)

Summary by CodeRabbit

Release Notes

• New Features
  • Validator detail pages now display a registration date field in the Overview section, showing when each validator was registered.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

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Run ID: 11a5da2c-eeda-4bcd-aa40-c501d3eb39c9

📥 Commits

Reviewing files that changed from the base of the PR and between 49f813c and fe88a35.

📒 Files selected for processing (2)

• apps/scan/app/[locale]/validators/[address]/page.tsx
• apps/scan/lib/api.ts

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📝 Walkthrough

Walkthrough

This PR adds validator registration date visibility by extending the validator detail page. The API layer now preserves the registered_at field when merging data from two validator endpoints, with fallback logic to ensure the field is available downstream. The UI layer conditionally displays the registration timestamp in the validator overview using the preserved field data.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately and concisely describes the main change: adding validator 'Registered' timestamp display on the detail page.
Description check	✅ Passed	The description is comprehensive with clear Summary, Test plan, and Related sections, though the Related section uses comments rather than explicit links.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/scan-validators-online-since

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