Fixed gemini system prompt handling

pkg/lmcli/provider/google/google.go

@@ -158,8 +158,14 @@ func createGenerateContentRequest(
 	}
 
 	request := &GenerateContentRequest{
-		Contents:           requestContents,
-		SystemInstructions: system,
+		Contents:          requestContents,
+		SystemInstruction: Content{
+			Parts: []ContentPart{
+				{
+					Text: system,
+				},
+			},
+		},
 		GenerationConfig: &GenerationConfig{
 			MaxOutputTokens: &params.MaxTokens,
 			Temperature:     &params.Temperature,

pkg/lmcli/provider/google/types.go

@@ -34,10 +34,10 @@ type GenerationConfig struct {
 }
 
 type GenerateContentRequest struct {
-	Contents           []Content         `json:"contents"`
-	Tools              []Tool            `json:"tools,omitempty"`
-	SystemInstructions string            `json:"systemInstructions,omitempty"`
-	GenerationConfig   *GenerationConfig `json:"generationConfig,omitempty"`
+	Contents          []Content         `json:"contents"`
+	Tools             []Tool            `json:"tools,omitempty"`
+	SystemInstruction Content           `json:"systemInstruction,omitempty"`
+	GenerationConfig  *GenerationConfig `json:"generationConfig,omitempty"`
 }
 
 type Candidate struct {