Add Vertex AI support

internal/config/config.go

@@ -48,6 +48,8 @@ type ProviderEntry struct {
 	APIKey     string `yaml:"api_key"`
 	Endpoint   string `yaml:"endpoint"`
 	APIVersion string `yaml:"api_version"`
+	Project    string `yaml:"project"`  // For Vertex AI
+	Location   string `yaml:"location"` // For Vertex AI
 }
 
 // ModelEntry maps a model name to a provider entry.
@@ -78,6 +80,12 @@ type AzureAnthropicConfig struct {
 	Model    string `yaml:"model"`
 }
 
+// VertexAIConfig contains Vertex AI-specific settings used internally by the Google provider.
+type VertexAIConfig struct {
+	Project  string `yaml:"project"`
+	Location string `yaml:"location"`
+}
+
 // Load reads and parses a YAML configuration file, expanding ${VAR} env references.
 func Load(path string) (*Config, error) {
 	data, err := os.ReadFile(path)