Fix date format example in reading settings

[giffeler]

What does this PR do?

Fixes the Reading settings date format example in the admin UI so it is rendered from the configured date format string instead of always showing the hard-coded January 23, 2026 example.

For example, yyyy-MM-dd now previews as 2026-01-23.

Closes #

Type of change

• Bug fix
• Feature (requires maintainer-approved Discussion)
• Refactor (no behavior change)
• Translation
• Documentation
• Performance improvement
• Tests
• Chore (dependencies, CI, tooling)

Checklist

• I have read CONTRIBUTING.md
• pnpm typecheck passes
• pnpm lint passes
• pnpm test passes (or targeted tests for my change)
• pnpm format has been run
• I have added/updated tests for my changes (if applicable)
• User-visible strings in the admin UI are wrapped for translation (if applicable). Do not include messages.po changes except in translation PRs — a workflow extracts catalogs on merge to main.
• I have added a changeset (if this PR changes a published package)
• New features link to an approved Discussion: https://github.com/emdash-cms/emdash/discussions/...

AI-generated code disclosure

• This PR includes AI-generated code — model/tool: GPT-5 Codex

Screenshots / test output

Validated with:

pnpm --filter @emdash-cms/admin typecheck
pnpm --filter @emdash-cms/admin exec vitest run tests/date-format-example.test.ts
pnpm changeset status --since=origin/main
pnpm exec prettier --check packages/admin/src/components/settings/GeneralSettings.tsx packages/admin/src/lib/date-format-example.ts packages/admin/tests/date-format-example.test.ts .changeset/fix-admin-date-format-example.md

I did not run the full repository lint or full test suite; this PR is scoped to the admin date format preview helper and its targeted test.

[changeset-bot]

🦋 Changeset detected

Latest commit: e37a31b

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 14 packages

Name	Type
@emdash-cms/admin	Patch
emdash	Patch
@emdash-cms/cloudflare	Patch
@emdash-cms/sandbox-workerd	Patch
@emdash-cms/fixture-perf-site	Patch
@emdash-cms/perf-demo-site	Patch
@emdash-cms/cache-demo-site	Patch
@emdash-cms/auth	Patch
@emdash-cms/blocks	Patch
@emdash-cms/gutenberg-to-portable-text	Patch
@emdash-cms/x402	Patch
create-emdash	Patch
@emdash-cms/auth-atproto	Patch
@emdash-cms/plugin-embeds	Patch

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[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[giffeler]

I have read the CLA Document and I hereby sign the CLA

[giffeler]

recheck