fix(measurements): bound the per-night sleep list to a year ending at to

The sleep list capped its read to the last year only when no `from`
was sent. An explicit early `from` walked every per-stage row back to
that date, on a multi-source account several rows per night for years.

The read window is now at most a year ending at `to` (or now). `from`
narrows it but never widens it, older nights are reached by moving
`to` back, and `meta.windowFrom` names the instant a cut window
started, so a client can tell a cut from an empty history.

src/lib/openapi/routes/measurements.ts

@@ -389,6 +389,12 @@ const listMeasurementsMeta = z
       .describe(
         "Rows discarded by the cross-source canonical picker on the day-collapse mode.",
       ),
+    windowFrom: z.iso
+      .datetime({ offset: true })
+      .optional()
+      .describe(
+        "Set on the per-night SLEEP_DURATION mode when the requested window was longer than 365 days: the instant the read started from. The window is a year ending at `to` (or now); page further back by moving `to`.",
+      ),
   })
   .meta({ id: "ListMeasurementsMeta" });