Let the lease key name its ask and time, and the user-list key say the lease is handed

ADR 0582 clause 3 writes the key holder "with the why, the ask and the time": LeaseHolder gains ask and at,
which LeaseHandedAway ignores (it reads handed-to alone). The grants part's user-list key gains lease-handed,
so the bus node's engine follows the grants part's list alone once the lease is handed (ADR 0571 clause 8)
and never falls back to the controller's; a key written before reads false.

Tests: a row in the lease table of TestTheCopiedComposerComposesAsTheControllers; the old key (shaped as
EncodeGrantsUserList writes it today) and the flag's round trip added to the existing user-list case in
delivery_test.go; no new test function.

(issue 774, 774/S3)

Claude-Session: https://claude.ai/code/session_01NcbgfJ9Gum47zkFKWRaovL

go/buscompose/buscompose_test.go

@@ -561,6 +561,9 @@ func TestTheCopiedComposerComposesAsTheControllers(t *testing.T) {
 		}{
 			{"a controller holds it", `{"instance":"novox/1234/2026-10-27T20:00:00Z","epoch":57}`, true, nil, false},
 			{"handed away", `{"handed-to":"the operator's hand-over","handed-by":"person.jochen"}`, true, nil, true},
+			// ADR 0582 clause 3 (774/S3): the write names the ask and the time, which turn nothing.
+			{"handed to mesh-grants with its ask and time", `{"handed-to":"mesh-grants","handed-by":"person.jochen","why":"w",` +
+				`"ask":"lease-write-1","at":"2026-11-02T10:00:00Z"}`, true, nil, true},
 			{"expired or deleted", ``, false, nil, false},
 			{"unreadable", ``, false, errors.New("refused"), false},
 			{"not a holder", `[1]`, true, nil, false},