feat(fitness): cache more fitness shells & show unsynced workouts on history

Precache:
- Service worker now precaches /fitness/workout(/active) shells (DE+EN)
  on install so a fresh device can log workouts offline without first
  visiting /fitness online.
- Layout-level precache adds /fitness/__data.json itself plus the
  static sub-routes nutrition/meals and check-in/body-parts (DE+EN).

Unsynced workouts on history:
- History page reads the offline outbox via getQueuedSessions on mount
  and merges queued sessions into the displayed list, sorted by
  startTime. Duration is computed locally so the Clock stat still
  shows.
- SessionCard gains an 'unsynced' prop: renders as a non-clickable
  div with an orange-accent border and a CloudOff badge labelled
  'Unsynced' / 'Nicht synchronisiert'.
- On window 'online', the page waits briefly for the layout's
  flushQueue to drain the outbox, then re-reads the queue and calls
  invalidateAll to swap unsynced placeholders for the now-saved
  server sessions.

src/lib/i18n/fitness/de.ts

@@ -33,6 +33,7 @@ export const de = {
 	weight: "Gewicht",
 	history_title: "Verlauf",
 	no_workouts_yet: "Noch keine Trainings. Starte dein erstes Training!",
+	unsynced_label: "Nicht synchronisiert",
 	load_more: "Mehr laden",
 	date: "Datum",
 	time: "Uhrzeit",