fix(registry): remove unstable kiro-auto model

- Removes kiro-auto from static model registry
- Removes kiro-auto mapping from executor
- Fixes compatibility issues reported in #7

Fixes #7

internal/registry/model_definitions.go

@@ -1195,17 +1195,6 @@ func GetGitHubCopilotModels() []*ModelInfo {
 // GetKiroModels returns the Kiro (AWS CodeWhisperer) model definitions
 func GetKiroModels() []*ModelInfo {
 	return []*ModelInfo{
-		{
-			ID:                  "kiro-auto",
-			Object:              "model",
-			Created:             1732752000, // 2024-11-28
-			OwnedBy:             "aws",
-			Type:                "kiro",
-			DisplayName:         "Kiro Auto",
-			Description:         "Automatic model selection by AWS CodeWhisperer",
-			ContextLength:       200000,
-			MaxCompletionTokens: 64000,
-		},
 		{
 			ID:                  "kiro-claude-opus-4.5",
 			Object:              "model",

internal/runtime/executor/kiro_executor.go

@@ -547,8 +547,6 @@ func kiroCredentials(auth *cliproxyauth.Auth) (accessToken, profileArn string) {
 // Agentic variants (-agentic suffix) map to the same backend model IDs.
 func (e *KiroExecutor) mapModelToKiro(model string) string {
 	modelMap := map[string]string{
-		// Proxy format (kiro- prefix)
-		"kiro-auto":              "auto",
 		"kiro-claude-opus-4.5":   "claude-opus-4.5",
 		"kiro-claude-sonnet-4.5": "claude-sonnet-4.5",
 		"kiro-claude-sonnet-4":   "claude-sonnet-4",