fix: the Yaesu keyer refused to send — a status reply we read too strictly

"the keyer buffer stayed full for 4s" and nothing keyed, on a rig whose CAT is
working. The buffer was not full: the check demanded the reply be exactly "KY0;"
with the digit at byte 2, so anything the FTDX10 phrases differently — a space
before the digit, another command's reply arriving first — read as "still full"
on every poll until the deadline.

The test is now asymmetric on purpose: only a clear "1" holds the send back.
Anything unrecognised goes ahead. Refusing to transmit because a status line was
phrased unexpectedly is the worse failure — the operator gets silence with no
explanation, where at worst sending early truncates a long message, which the
chunk loop then recovers from.

The reply is also logged once per run, since we have no verified sample of it —
that line is what turns the next surprise into a fact instead of a theory.

internal/cat/yaesu_cw_test.go

@@ -61,3 +61,34 @@ func TestYaesuCWChunking(t *testing.T) {
 		t.Errorf("chunks rejoin to %q, want %q", joined, msg)
 	}
 }
+
+// Reading the KY status reply.
+//
+// The first version demanded exactly "KY0;" with the digit at byte 2, and on a
+// real FTDX10 that refused to send at all: the reply was phrased differently,
+// every poll read as "still full", and after four seconds the send gave up
+// having keyed nothing. Hence the asymmetry — only a clear "1" blocks.
+func TestYaesuCWBufferFull(t *testing.T) {
+	cases := []struct {
+		reply string
+		full  bool
+	}{
+		{"KY0;", false},
+		{"KY1;", true},
+		{"KY 0;", false}, // a space before the digit
+		{"KY 1;", true},
+		{"ky1;", true}, // lower case
+		{" KY0; ", false},
+		// Shapes we have no sample of must NOT block: silence with no explanation
+		// is a worse failure than sending a moment early.
+		{"KY;", false},
+		{"", false},
+		{"FA014074000;", false}, // another command's reply arriving first
+		{"KYX;", false},
+	}
+	for _, c := range cases {
+		if got := yaesuCWBufferFull(c.reply); got != c.full {
+			t.Errorf("yaesuCWBufferFull(%q) = %v, want %v", c.reply, got, c.full)
+		}
+	}
+}