llm/ant: add Claude 4 sonnet/opus

Not set as default yet.
There's a bit of prompt engineering work
to do before we flip the switch.
diff --git a/llm/llm_string.go b/llm/llm_string.go
index 1c3189e..44f9ac8 100644
--- a/llm/llm_string.go
+++ b/llm/llm_string.go
@@ -73,11 +73,12 @@
 	_ = x[StopReasonMaxTokens-12]
 	_ = x[StopReasonEndTurn-13]
 	_ = x[StopReasonToolUse-14]
+	_ = x[StopReasonRefusal-15]
 }
 
-const _StopReason_name = "StopReasonStopSequenceStopReasonMaxTokensStopReasonEndTurnStopReasonToolUse"
+const _StopReason_name = "StopReasonStopSequenceStopReasonMaxTokensStopReasonEndTurnStopReasonToolUseStopReasonRefusal"
 
-var _StopReason_index = [...]uint8{0, 22, 41, 58, 75}
+var _StopReason_index = [...]uint8{0, 22, 41, 58, 75, 92}
 
 func (i StopReason) String() string {
 	i -= 11