perf: add Server-Timing, split fitness bundle, tighten DB queries

- Add `timing` handle in hooks.server.ts emitting Server-Timing headers
  and expose `locals.timing.mark/measure` for per-load instrumentation.
- Drop dead `getEnrichedExerciseById` fallback in fitness detail page —
  server load already 404s via errorWithVerse, so the client no longer
  pulls exercisedb-raw.json (~760KB) into the detail bundle.
- Add `{ createdBy: 1, nextExecutionDate: -1 }` index on RecurringPayment
  for user-scoped list queries.
- Narrow populate projections in cospend/debts (title/date/category on
  userSplits, _id only on allRelatedSplits) to cut payload + hydration.
- Parallelize today's sessions + WorkoutSchedule lookup in the nutrition
  page load via Promise.all; add `.lean()` + `.select('templateId')` to
  the lastScheduled query.

src/routes/api/cospend/debts/+server.ts

@@ -31,7 +31,7 @@ export const GET: RequestHandler = async ({ locals }) => {
   try {
     // Get all splits for the current user
     const userSplits = await PaymentSplit.find({ username: currentUser })
-      .populate('paymentId')
+      .populate('paymentId', 'title date category _id')
       .lean();
 
     // Get all other users who have splits with payments involving the current user
@@ -40,7 +40,7 @@ export const GET: RequestHandler = async ({ locals }) => {
       paymentId: { $in: paymentIds } as any,
       username: { $ne: currentUser }
     })
-      .populate('paymentId')
+      .populate('paymentId', '_id')
       .lean();
 
     // Group debts by user

src/routes/fitness/[exercises=fitnessExercises]/[id]/+page.svelte

@@ -1,6 +1,5 @@
 <script>
 	import { page } from '$app/stores';
-	import { getEnrichedExerciseById } from '$lib/data/exercisedb';
 
 	/** @param {string | undefined | null} type @param {'en'|'de'} lang */
 	function exerciseTypeInfo(type, lang) {
@@ -20,7 +19,6 @@
 				return null;
 		}
 	}
-	import { localizeExercise, translateTerm } from '$lib/data/exercises';
 	import { detectFitnessLang, fitnessSlugs, t } from '$lib/js/fitnessI18n';
 	import { ChevronRight } from '@lucide/svelte';
 
@@ -54,7 +52,7 @@
 
 	let activeTab = $state('about');
 
-	const exercise = $derived(data.exercise ?? getEnrichedExerciseById($page.params.id, lang));
+	const exercise = $derived(data.exercise);
 	const typeInfo = $derived(exerciseTypeInfo(exercise?.exerciseType, lang));
 	const similar = $derived(data.similar ?? []);
 	const history = $derived(data.history?.history ?? []);

src/routes/fitness/[nutrition=fitnessNutrition]/[[date=fitnessDate]]/+page.server.ts

@@ -19,10 +19,13 @@ export const load: PageServerLoad = async ({ fetch, params, locals }) => {
 		try {
 			const user = await requireAuth(locals);
 			await dbConnect();
-			const sessions = await WorkoutSession.find({
-				createdBy: user.nickname,
-				startTime: { $gte: dayStart, $lte: dayEnd }
-			}).select('kcalEstimate').lean();
+			const [sessions, schedule] = await Promise.all([
+				WorkoutSession.find({
+					createdBy: user.nickname,
+					startTime: { $gte: dayStart, $lte: dayEnd }
+				}).select('kcalEstimate').lean(),
+				WorkoutSchedule.findOne({ userId: user.nickname }).lean()
+			]);
 			let kcal = 0;
 			for (const s of sessions) {
 				if (s.kcalEstimate?.kcal) kcal += s.kcalEstimate.kcal;
@@ -31,12 +34,11 @@ export const load: PageServerLoad = async ({ fetch, params, locals }) => {
 			// If no exercise done today, project kcal from the next scheduled template
 			let projected = null;
 			if (kcal === 0) {
-				const schedule = await WorkoutSchedule.findOne({ userId: user.nickname });
 				if (schedule?.templateOrder?.length) {
 					const lastScheduled = await WorkoutSession.findOne({
 						createdBy: user.nickname,
 						templateId: { $in: schedule.templateOrder }
-					}).sort({ startTime: -1 });
+					}).sort({ startTime: -1 }).select('templateId').lean();
 
 					let nextId;
 					if (!lastScheduled?.templateId) {