Scheduler Event Timeline Localization

Override timeline toolbar and overlay strings for localization.

• Localized prev/next/today labels on timeline chrome
• Matching calendar and timeline copy in multilingual apps

• Provide SchedulerLocaleText via SchedulerChromeContext or the locale_text prop.
• Wrap the tree in DatetimeLocale when editing uses pickers.
• Update the locale text signal when the user picks a language.