[1141] Add locale-aware display date adapter

[Chris0Jeky]

Summary

• add a pure adapter for locale-explicit instant date, date-time, and time formatting
• keep persisted YYYY-MM-DD calendar keys on the existing UTC-safe due-date path
• return null for absent, invalid, or calendar/instant type-mismatch input

Proof

• red-first focused run failed before the new utility existed with the expected unresolved import
• focused display-date suite: 12 passed
• existing due-date suite with the adapter: 21 passed
• explicit en/it/es locale, leap-day, invalid-input, and UTC/Pacific near-midnight coverage
• npm run lint (8 pre-existing warnings, 0 errors)
• npm run typecheck
• npm run build (known ineffective dynamic-import warning only)
• git diff --check

Refs #1141

No issue close or merge requested; this PR is intentionally left open for review.

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