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/routes/fitness/+layout.svelte

@@ -4,7 +4,7 @@
 	import Header from '$lib/components/Header.svelte';
 	import UserHeader from '$lib/components/UserHeader.svelte';
 	import LanguageSelector from '$lib/components/LanguageSelector.svelte';
-	import { BarChart3, Clock, Dumbbell, ListChecks, Ruler, UtensilsCrossed } from '@lucide/svelte';
+	import { BarChart3, Clock, Dumbbell, ListChecks, NotebookPen, UtensilsCrossed } from '@lucide/svelte';
 	import { getWorkout } from '$lib/js/workout.svelte';
 	import { getWorkoutSync } from '$lib/js/workoutSync.svelte';
 	import WorkoutFab from '$lib/components/fitness/WorkoutFab.svelte';
@@ -27,7 +27,7 @@
 		const slugs = [
 			'workout', 'training', 'workout/active', 'training/aktiv',
 			'exercises', 'uebungen', 'stats', 'statistik',
-			'history', 'verlauf', 'measure', 'messen',
+			'history', 'verlauf', 'check-in', 'erfassung',
 			'nutrition', 'ernaehrung'
 		];
 		const urls = slugs.map((s) => `/fitness/${s}`);
@@ -69,7 +69,7 @@
 		!$page.url.pathname.startsWith(`/fitness/${s.nutrition}/meals`)
 	);
 	const isMeasureIndex = $derived(
-		/^\/fitness\/(measure|messen)\/?$/.test($page.url.pathname)
+		/^\/fitness\/(check-in|erfassung)\/?$/.test($page.url.pathname)
 	);
 	/** @param {number} secs */
 	function formatElapsed(secs) {
@@ -86,7 +86,7 @@
 			<li style="--active-fill: var(--nord13)"><a href="/fitness/{s.history}" class:active={isActive(`/fitness/${s.history}`)}><Clock size={16} strokeWidth={1.5} class="nav-icon" /><span class="nav-label">{labels.history}</span></a></li>
 			<li style="--active-fill: var(--nord8)"><a href="/fitness/{s.workout}" class:active={isActive(`/fitness/${s.workout}`)}><Dumbbell size={16} strokeWidth={1.5} class="nav-icon" /><span class="nav-label">{labels.workout}</span></a></li>
 			<li style="--active-fill: var(--nord14)"><a href="/fitness/{s.exercises}" class:active={isActive(`/fitness/${s.exercises}`)}><ListChecks size={16} strokeWidth={1.5} class="nav-icon" /><span class="nav-label">{labels.exercises}</span></a></li>
-			<li style="--active-fill: var(--nord12)"><a href="/fitness/{s.measure}" class:active={isActive(`/fitness/${s.measure}`)}><Ruler size={16} strokeWidth={1.5} class="nav-icon" /><span class="nav-label">{labels.measure}</span></a></li>
+			<li style="--active-fill: var(--nord12)"><a href="/fitness/{s.measure}" class:active={isActive(`/fitness/${s.measure}`)}><NotebookPen size={16} strokeWidth={1.5} class="nav-icon" /><span class="nav-label">{labels.measure}</span></a></li>
 			<li style="--active-fill: var(--nord15)"><a href="/fitness/{s.nutrition}" class:active={isActive(`/fitness/${s.nutrition}`)}><UtensilsCrossed size={16} strokeWidth={1.5} class="nav-icon" /><span class="nav-label">{labels.nutrition}</span></a></li>
 		</ul>
 	{/snippet}