feat(fitness): rename Measure route to Check-in / Erfassung (NotebookPen icon)

Route slugs and nav label rename only — storage, API endpoints
(`/api/fitness/measurements`), and the `BodyMeasurement` Mongo model
keep their technical names.

- `/fitness/measure` → `/fitness/check-in` (EN)
- `/fitness/messen` → `/fitness/erfassung` (DE)
- Folder `[measure=fitnessMeasure]` → `[checkin=fitnessCheckIn]`
  (git rename; history preserved).
- Param matcher `fitnessMeasure.ts` → `fitnessCheckIn.ts`, accepts
  `check-in` / `erfassung`.
- `fitnessSlugs(lang).measure` and `fitnessLabels(lang).measure` code
  keys are unchanged — value returns "check-in"/"erfassung" and
  "Check-in"/"Erfassung" respectively, so no call site needs touching.
- slugMap language-detection updated to `erfassung ↔ check-in`.
- Service-worker cache list + the layout regex that gates the wider
  content width now reference the new slugs.
- Nav icon swapped from `Ruler` to `NotebookPen` — reads as "logging
  entries" and spans weight / composition / period better.

Bookmarks on the old URLs will 404; no redirect added.

src/lib/js/fitnessI18n.ts

@@ -1,8 +1,8 @@
 /** Fitness route i18n — slug mappings and UI translations */
 
 const slugMap: Record<string, Record<string, string>> = {
-	en: { statistik: 'stats', verlauf: 'history', training: 'workout', aktiv: 'active', uebungen: 'exercises', messen: 'measure', ernaehrung: 'nutrition' },
-	de: { stats: 'statistik', history: 'verlauf', workout: 'training', active: 'aktiv', exercises: 'uebungen', measure: 'messen', nutrition: 'ernaehrung' }
+	en: { statistik: 'stats', verlauf: 'history', training: 'workout', aktiv: 'active', uebungen: 'exercises', erfassung: 'check-in', ernaehrung: 'nutrition' },
+	de: { stats: 'statistik', history: 'verlauf', workout: 'training', active: 'aktiv', exercises: 'uebungen', 'check-in': 'erfassung', nutrition: 'ernaehrung' }
 };
 
 const germanSlugs = new Set(Object.keys(slugMap.en));
@@ -31,7 +31,7 @@ export function fitnessSlugs(lang: 'en' | 'de') {
 		workout: lang === 'en' ? 'workout' : 'training',
 		active: lang === 'en' ? 'active' : 'aktiv',
 		exercises: lang === 'en' ? 'exercises' : 'uebungen',
-		measure: lang === 'en' ? 'measure' : 'messen',
+		measure: lang === 'en' ? 'check-in' : 'erfassung',
 		nutrition: lang === 'en' ? 'nutrition' : 'ernaehrung'
 	};
 }
@@ -43,7 +43,7 @@ export function fitnessLabels(lang: 'en' | 'de') {
 		history: lang === 'en' ? 'History' : 'Verlauf',
 		workout: lang === 'en' ? 'Workout' : 'Training',
 		exercises: lang === 'en' ? 'Exercises' : 'Übungen',
-		measure: lang === 'en' ? 'Measure' : 'Messen',
+		measure: lang === 'en' ? 'Check-in' : 'Erfassung',
 		nutrition: lang === 'en' ? 'Nutrition' : 'Ernährung'
 	};
 }