fix(awards): stack the reference validity dates, and prove the award fallback

Two dates side by side put each one in a half-width Field2, which spends 120px
on its label column — the second label overlapped the first input and the row
ran off the panel. The comment ten lines above says exactly this about the
group/subgroup fields; one per row, as everything else in this editor.

Also shows a far-future end date as open-ended. RDA carries 9999-12-31 as "no
end" and printing it back reads like a real deadline.

The claim that an empty per-reference window inherits the award's is now a
test rather than a comment: a QSO before the award's own ValidFrom does not
count for a reference that has no window of its own, and a narrower reference
window still applies on top.

internal/award/refvalidity_test.go

@@ -76,3 +76,34 @@ func TestExpiredRefStopsCountingForLaterQSOs(t *testing.T) {
 		t.Errorf("a reference with no window is unaffected: got %v", got)
 	}
 }
+
+// The claim that an empty per-reference window "inherits the award's" has to be
+// a fact about the code, not a comment. Compute and MatchQSO both gate on
+// inScope, which enforces the award's own dates — so a reference with no window
+// of its own is already bounded by them, and duplicating the check per reference
+// would only create a second place for the same dates to disagree.
+func TestEmptyRefWindowInheritsTheAward(t *testing.T) {
+	d := Def{
+		Code: "RDA", Name: "Russian District Award", Valid: true,
+		Type: TypeQSOFields, Field: "note", MatchBy: "code",
+		Confirm:   []string{"lotw"},
+		ValidFrom: "1991-06-12", // the award itself starts here
+	}
+	metas := []RefMeta{{Code: "KL-04", Name: "Kostomuksha", Valid: true}} // no window of its own
+
+	q := func(on string) *qso.QSO {
+		return &qso.QSO{Callsign: "RA1ABC", Band: "20m", Notes: "KL-04", QSODate: day(on)}
+	}
+	if got := MatchQSO(d, metas, q("1991-06-11")); len(got) != 0 {
+		t.Errorf("a QSO before the AWARD's start counted for a reference with no window of its own: %v", got)
+	}
+	if got := MatchQSO(d, metas, q("1991-06-12")); len(got) != 1 {
+		t.Errorf("a QSO on the award's first day must count: %v", got)
+	}
+
+	// And a reference window NARROWER than the award's still applies on top.
+	metas[0].ValidTo = "2025-08-31"
+	if got := MatchQSO(d, metas, q("2025-09-01")); len(got) != 0 {
+		t.Errorf("the reference's own end date was ignored: %v", got)
+	}
+}