Replaces the raw "1915-08 · 5" aria-label, which a screen reader
announces as "1915 dash 08 middle dot 5", with the i18n template
timeline_bar_aria("{when}, {count} ...") and a getLocale-formatted
month/year string. Closes Leonie's WCAG 1.3.1 / 4.1.2 finding and
Felix's localisation flag.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>