feat(fitness/measure): paginate past measurements (SSR 10, "Show more" pulls 20)

SSR now ships only the 10 most recent measurements (down from 200) to
cut initial page weight. A "Show more (N/total)" pill appears below
the list when more are available; clicking fetches the next 20 via
the existing GET endpoint (offset/limit already supported) and
appends with dedupe by `_id`.

`measurementsTotal` is seeded from the API's `total` field and kept
in sync on save (+1) / delete (−1). The button is hidden when the
history is collapsed or when `measurements.length >= total`.

Added `show_more` i18n string.

src/lib/js/fitnessI18n.ts

@@ -312,6 +312,7 @@ const translations: Translations = {
 	body_fat_pct: { en: 'Body Fat (%)', de: 'Körperfett (%)' },
 	history: { en: 'History', de: 'Verlauf' },
 	past_measurements: { en: 'Past measurements', de: 'Frühere Messungen' },
+	show_more: { en: 'Show more', de: 'Mehr anzeigen' },
 
 	// SetTable
 	set_header: { en: 'SET', de: 'SATZ' },