web: add deterministic Drand countdown boundary tests

[karagozemin]

Summary

Add deterministic boundary tests for the Drand countdown used by the web dashboard.

Why this matters

The countdown is central to the reveal UX, but its time calculation currently lives inside a React hook and depends directly on Date.now(). Existing component tests cover rendered copy, not the exact before-R / at-R / past-R math or offline fallback behavior.

Scope

• Extract the countdown calculation into a small pure helper that accepts target round, current time, genesis, and period.
• Reuse the helper for both live chain info and the offline quicknet fallback in useDrandCountdown.
• Add Node-based unit tests with fixed timestamps; no browser, live Drand call, or real timers.
• Keep the existing UI and polling cadence unchanged.

Acceptance criteria

• Tests cover one second before R, exactly at R, and after R.
• Published rounds report secondsRemaining: 0.
• Future rounds report the correct target time and remaining seconds.
• formatCountdown has boundary cases for seconds, minutes, and hours.
• The new test is included in pnpm web:test; web typecheck passes.

[oyebolarotimi269-ai]

@oyebolarotimi269-ai has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

please assign this issue to me

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[ogundeleoluwaferanmi35]

@ogundeleoluwaferanmi35 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Please assign this issue to me, I can get it done in 30 mins

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