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.

package.json

@@ -1,6 +1,6 @@
 {
 	"name": "homepage",
-	"version": "1.37.2",
+	"version": "1.37.3",
 	"private": true,
 	"type": "module",
 	"scripts": {