Fix deterministic editorial date formatting

[xrendan]

Summary

• centralize editorial date formatting in the America/Toronto timezone
• use the shared formatter for memo cards, memo engagement, feed cards, and state-of-the-nation chart labels
• preserve date-only chart periods by anchoring them at noon UTC before Toronto formatting

Why

React hydration error 418 was caused by server and browser renders selecting different calendar days for the same timestamp. Recent PostHog samples reference an older cached bundle, but additional unpinned client date formatters remained in the current code.

Validation

• pnpm exec tsc --noEmit --incremental false
• targeted ESLint: no errors; one existing no-img-element warning in the Open Graph chart renderer
• formatter output matched under UTC, America/Edmonton, and Asia/Tokyo

[greptile-apps]

Greptile Summary

Centralizes editorial date rendering around an America/Toronto formatter to prevent server/client calendar-day differences.

• Adds shared short-date, long-date, and month-year formatting helpers with invalid-value handling.
• Anchors date-only values at noon UTC so chart periods retain their intended Toronto calendar date.
• Applies the shared helpers to memo, engagement, feed, canvas-chart, and Open Graph labels.

Confidence Score: 5/5

The PR appears safe to merge, with the affected date paths consistently using the intended editorial timezone.

The shared formatter handles invalid inputs, preserves date-only chart periods, and runs on supported Node.js and browser targets; no concrete blocking or non-blocking defect remains.

Important Files Changed

Filename	Overview
src/lib/date-format.ts	Introduces deterministic Toronto date formatters and safely preserves bare calendar dates through noon-UTC anchoring.
src/app/memos/[slug]/MemoEngagement.tsx	Replaces UTC engagement-date formatting with the shared editorial timezone behavior.
src/app/state-of-the-nation/canvas/OverlayChart.tsx	Routes monthly tooltip labels through the shared deterministic formatter.
src/app/state-of-the-nation/og-card.tsx	Uses shared month formatting for chart labels while retaining the annual fallback for invalid or absent dates.
src/app/memos/types.ts	Makes memo-list date formatting deterministic across server and browser rendering.
src/components/feed/types.ts	Makes feed-card publication dates deterministic in the editorial timezone.
src/components/ui/memo-card.tsx	Consolidates existing Toronto memo-card formatting into the shared helper without changing fallback behavior.

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