Localize calendar date pickers to the active UI locale

[paulocastellano]

Summary

Several calendar widgets hardcode locale="en" (or rely on the Reka UI English default), so month/weekday names stay English even when the app UI locale is Ukrainian, Portuguese, Japanese, etc.

This was spotted while shipping Ukrainian as a full platform locale (#219). It is shared debt across all non-English locales — not a Ukrainian-only gap — and should be fixed separately from that PR.

Where it shows up

Component	Hardcoded?	Product surfaces
resources/js/components/DatePicker.vue	locale="en" on <Calendar>	Posts → Calendar (jump to date); Settings → API Keys (expiry)
resources/js/components/posts/PickTimePopover.vue	locale="en" + calendar-label="Pick a date"	Post editor → schedule date/time
resources/js/components/ui/date-range-picker/DateRangePicker.vue	No explicit locale (Reka default, likely EN)	Analytics; Automations → Metrics

Not affected: the weekly grid on Posts → Calendar already uses dayjs and follows the active UI locale.

Expected behavior

Calendar month names, weekday headers, and accessibility labels should follow page.props.locale / the dayjs locale already configured in resources/js/dayjs.ts (including uk and every other supported language).

Suggested approach

1. Pass the active app locale into DatePicker / PickTimePopover / DateRangePicker (from Inertia locale or dayjs).
2. Map app codes to Reka/dayjs locale codes where needed (pt-BR → pt-BR / pt-br).
3. Localize hardcoded English strings like calendar-label="Pick a date" / "Date picker" via $t(...).
4. Spot-check with at least one Cyrillic (uk/ru) and one Latin (pt-BR/de) UI locale.

Out of scope (related but separate)

• MetricsGrid keyword matching still mostly en/pt/es
• AI post templates only ship for en / es / pt-BR (others fall back to English)

Related

• Add Ukrainian as a supported platform language #219 — Add Ukrainian as a supported platform language