feat(coach): name a read past the lookback limit on the trail

A read whose readings all lie past the lookback limit was reported on its
step as outside_window, and its fetch entry carried no reason, so a client
could not tell an empty window from data the limit keeps out. The step now
carries reason outside_reach and the fetch entry mirrors it. The method
line and the web trail keep the window sentence; the answer names the
limit as before.

src/components/insights/coach-panel/__tests__/turn-activity.test.tsx

@@ -102,6 +102,14 @@ describe("describeStep", () => {
     ]);
   });
 
+  it("keeps the window sentence on a read past the lookback limit", () => {
+    const reach: CoachStep = { ...SLEEP, reason: "outside_reach" };
+    expect(describeStep(reach, t, tCount).meta).toEqual([
+      "last 30 days",
+      "no readings in this window",
+    ]);
+  });
+
   it("counts metrics on the snapshot step and rows on labs", () => {
     const snapshot: CoachStep = {
       id: "s1",