feat(fitness/measure): consolidate entries by day + richer past-measurements summary

- Server POST now upserts by (user, calendar day). Non-conflicting
  fields merge silently; real overwrites (new non-empty value ≠
  stored value) return 409 with the conflict list. Client retries
  with `?overwrite=1` after a confirm dialog naming each field and
  its old→new value. Null/empty payload fields are skipped, so
  logging a body-fat entry on a day that already has weight merges
  cleanly without flagging a phantom weight conflict.
- `summaryParts` in the history now includes a body-parts count,
  e.g. "86 kg · 0.1% bf · 5 body parts" or "5 body parts" instead
  of the flat "Body measurements only" fallback. Pluralised in EN
  and DE.
- Inline quick-edit: "Full edit →" text replaced by a dashed primary
  pill `Pencil · Edit all fields · ChevronRight`, inlined with the
  X / ✓ action buttons on the same row. The label collapses to
  icons only at ≤480px so the three controls stay on one line.
- Quick-edit date input swapped from native `<input type="date">`
  to the site's `DatePicker` component.
- New i18n: `overwrite_title`, `overwrite_message`, `overwrite_confirm`.
- TODO.md marks features #2 and #3 done. CLAUDE.md carries a
  policy note (no AI-attribution trailers on commits).

src/lib/js/fitnessI18n.ts

@@ -313,6 +313,12 @@ const translations: Translations = {
 	history: { en: 'History', de: 'Verlauf' },
 	past_measurements: { en: 'Past measurements', de: 'Frühere Messungen' },
 	show_more: { en: 'Show more', de: 'Mehr anzeigen' },
+	overwrite_title: { en: 'Overwrite existing values?', de: 'Bestehende Werte überschreiben?' },
+	overwrite_message: {
+		en: 'You already have values for this date: {fields}. Replace them?',
+		de: 'Für dieses Datum sind bereits Werte erfasst: {fields}. Überschreiben?'
+	},
+	overwrite_confirm: { en: 'Overwrite', de: 'Überschreiben' },
 
 	// SetTable
 	set_header: { en: 'SET', de: 'SATZ' },