Improve custom recurrence dialog UI and native date/time fields

[christenbc]

Summary

• Reworks the Custom recurrence dialog so frequency-specific options are clearer: Interval and Days of week descriptions update with the selected frequency, weekday checkboxes stay on one row with more space below the description, and Monthly/Yearly/End condition choices grey out controls that no longer apply.
• Fixes radio button rendering in Chromium by using a real sibling element for the selected dot (pseudo-elements on <input> are not painted).
• Wires existing i18n keys through the modal so labels, descriptions, and end-condition text use translations instead of hardcoded English.
• Introduces shared tn-datetime-input styling (padding, subtle border, rounded corners) on native date/time fields in the recurrence dialog, date/time picker, timeblock creation, and reminder modals.

Test plan

• Open Custom recurrence from a recurring task and confirm Interval/Days of week descriptions change when switching Daily / Weekly / Monthly / Yearly.
• Confirm weekday checkboxes render on one row with comfortable spacing below the description.
• In Monthly and Yearly sections, switch between “on date” and “on the Nth weekday” and confirm only the active dropdowns are editable.
• In End condition, switch Never / After N / Until date and confirm inactive inputs are greyed out.
• Confirm radio buttons show a ring with a centered dot when selected (unchecked = ring only).
• Change Obsidian language (non-English) and confirm Custom recurrence strings are translated.
• Check start date/time fields in Custom recurrence match other modals’ native field styling.
• Spot-check date/time fields in Date/time picker, Timeblock creation, and Reminder (absolute date/time) for the same styling.
• npm run typecheck, npm run test, and npm run lint pass.