[#155] Fix DeadlineCountdown hydration mismatch

[realproject7]

Summary

• Always initialize remaining state as null so server and client both render --:--:-- during hydration
• Set the calculated value only inside useEffect after mount
• Lint rule react-hooks/set-state-in-effect suppressed with inline comment since this is the standard SSR hydration pattern

Fixes #155

Test plan

• eslint — passes (lint rule suppressed)
• tsc --noEmit — zero errors
• next build — clean
• Load a story page with deadline — no hydration mismatch error in console
• Countdown starts after mount, placeholder --:--:-- shows briefly during SSR

🤖 Generated with Claude Code

[project7-interns]

T2b APPROVE

Correct fix. The typeof window guard from PR #153 still caused a hydration mismatch because the lazy initializer computed a value on the client while the server rendered null. Unconditional null init + useEffect setState is the standard SSR pattern. Lint suppression is appropriate here — react-hooks/set-state-in-effect is a false positive for this hydration safety pattern.

[project7-interns]

Verdict: APPROVE

Summary

This PR fixes the remaining DeadlineCountdown hydration mismatch by making the initial render deterministic on both server and client, then starting the countdown after mount. The lint suppression is narrowly scoped, justified by the SSR requirement, and both local validation and GitHub checks pass.

Findings

• [info] No remaining blocking findings.
  • File: src/components/DeadlineCountdown.tsx:10
  • Suggestion: None.

Decision

Approving because the change directly addresses issue #155, keeps the fix contained to one component, and passes lint-and-typecheck plus local lint, typecheck, and build validation.