fix(measurements): tighten W7c grouped-view pagination and timezone comment

Self-review polish on top of the v1.4.37 W7c step-consolidation
landing:

- The collapsed daily view returns up to 5000 synthesised rows in
  one shot, so the legacy 25-row pagination would have re-fired the
  same scan with offset=0 returning the same slice. Disable
  pagination on the day-grouped path; per-sample lists keep their
  PAGE_SIZE=25 behaviour.
- Bump the per-page row scan from 1250 to the server max of 5000 so
  even chatty pre-drain Apple-Watch accounts (~200 chunks/day on
  busy days) get a useful number of daily rows on the first paint.
  Post-drain the scan is trivially short (each day reduces to one
  stats: row).
- Reset offset=0 explicitly on the grouped path so a sort-direction
  flip never paginates into an empty server slice.
- Clarify the day-boundary comment in the dayKey drill-down branch
  — the ±12h around canonical noon shift works for every IANA
  offset, including sub-half-hour zones (Asia/Kathmandu +5:45,
  Pacific/Chatham +12:45).

src/app/api/measurements/route.ts

@@ -87,7 +87,11 @@ export const GET = apiHandler(async (request: NextRequest) => {
     // Resolve `[dayStart, dayEnd)` for the requested calendar day in
     // the user's local zone. We piggy-back on `canonicalDailyTimestamp`
     // (which returns the local-noon instant) and shift ±12 h to land
-    // on the day boundary — works for whole-hour and half-hour zones.
+    // on the day boundary. Works for every IANA offset — including
+    // sub-half-hour zones like Asia/Kathmandu (UTC+5:45) and
+    // Pacific/Chatham (UTC+12:45) — because the noon instant already
+    // carries the zone's offset and the ±12 h shift is independent
+    // of it.
     const noonLocal = canonicalDailyTimestamp(dayKey, tz);
     const dayStart = new Date(noonLocal.getTime() - 12 * 60 * 60 * 1000);
     const dayEnd = new Date(noonLocal.getTime() + 12 * 60 * 60 * 1000);

src/components/measurements/measurement-list.tsx

@@ -234,10 +234,18 @@ export function MeasurementList({ onEdit, onAddFirst }: MeasurementListProps) {
       if (isCumulativeFilter) {
         params.set("groupBy", "day");
         // The collapsed mode synthesises one row per day from the
-        // window of raw samples — bump the per-page row scan so a
-        // wide history can render a full page of daily rows without
-        // missing back-fill from a chatty Apple-Watch day.
-        params.set("limit", String(Math.max(PAGE_SIZE * 50, 1000)));
+        // window of raw samples. Use the server-side ceiling (5000)
+        // so a chatty pre-drain Apple-Watch account (≈200 per-sample
+        // chunks/day on the busiest days) still fills several screens
+        // of daily rows before the nightly drain reduces each day to
+        // a single `stats:` row. Post-drain the scan is trivially
+        // short — every day reduces to 1 row.
+        params.set("limit", "5000");
+        // The synthesised rows live entirely in the collapse branch
+        // — pagination/offset don't apply on the server side. Reset
+        // the offset so a sort-direction flip doesn't paginate into
+        // an empty slice.
+        params.set("offset", "0");
       }
       const res = await fetch(`/api/measurements?${params}`);
       if (!res.ok) throw new Error("Failed to fetch");
@@ -321,7 +329,16 @@ export function MeasurementList({ onEdit, onAddFirst }: MeasurementListProps) {
     },
   });
 
-  const totalPages = data ? Math.ceil(data.meta.total / PAGE_SIZE) : 0;
+  // v1.4.37 W7c — the collapsed daily view paints up to 5000
+  // synthesised rows in one shot (one row per day for the
+  // configured window). Pagination would force a second server
+  // round-trip that re-fires the same scan, so the day-grouped
+  // path collapses to a single page. Per-sample lists continue to
+  // paginate at PAGE_SIZE = 25.
+  const totalPages =
+    data && !isCumulativeFilter
+      ? Math.ceil(data.meta.total / PAGE_SIZE)
+      : 0;
 
   function startEdit(measurement: Measurement) {
     if (onEdit) {