DJ-72: Deduplicate raw date formatting into shared formatDate util

[devin-ai-integration]

Summary

Fixes DJ-72. The raw new Date(x.createdAt).toDateString() expression ("Thu Jul 30 2026") was copy-pasted in ArticlePreview, ArticleMeta, and Comment. Added frontend/lib/utils/formatDate.ts:

const formatDate = (iso: string): string =>
  new Date(iso).toLocaleDateString("en-US", { year: "numeric", month: "long", day: "numeric" });

All three components now use formatDate(...), rendering dates like "July 30, 2026". No new dependencies; no toDateString() calls remain in frontend/components.

Verified with npm run build and by running backend + frontend locally.

Before

After

Article page after:

Link to Devin session: https://partner-workshops.devinenterprise.com/sessions/824a22b5019349bc9ea2b2b07ca45e05

[devin-ai-integration]

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