Refactor token management, client initialization, and project handling

- Consolidated `TokenStorage` struct into `internal/auth/models.go` for better organization.
- Updated `Client` to use `TokenStorage` for managing email and project ID.
- Simplified `SetupUser` method to ensure proper token and project assignment.
- Refactored API handlers to leverage new `GetEmail` and `GetProjectID` methods in `Client`.
- Cleanup: Removed unused structures and redundant code from `client.go` and `auth.go`.
- Adjusted CLI flow in `login.go` and `run.go` for streamlined user onboarding.

internal/client/models.go

@@ -0,0 +1,80 @@
+package client
+
+import "time"
+
+type ErrorMessage struct {
+	StatusCode int
+	Error      error
+}
+
+type GCPProject struct {
+	Projects []GCPProjectProjects `json:"projects"`
+}
+type GCPProjectLabels struct {
+	GenerativeLanguage string `json:"generative-language"`
+}
+type GCPProjectProjects struct {
+	ProjectNumber  string           `json:"projectNumber"`
+	ProjectID      string           `json:"projectId"`
+	LifecycleState string           `json:"lifecycleState"`
+	Name           string           `json:"name"`
+	Labels         GCPProjectLabels `json:"labels"`
+	CreateTime     time.Time        `json:"createTime"`
+}
+
+type Content struct {
+	Role  string `json:"role"`
+	Parts []Part `json:"parts"`
+}
+
+// Part represents a single part of a message's content.
+type Part struct {
+	Text             string            `json:"text,omitempty"`
+	InlineData       *InlineData       `json:"inlineData,omitempty"`
+	FunctionCall     *FunctionCall     `json:"functionCall,omitempty"`
+	FunctionResponse *FunctionResponse `json:"functionResponse,omitempty"`
+}
+
+type InlineData struct {
+	MimeType string `json:"mime_type,omitempty"`
+	Data     string `json:"data,omitempty"`
+}
+
+// FunctionCall represents a tool call requested by the model.
+type FunctionCall struct {
+	Name string                 `json:"name"`
+	Args map[string]interface{} `json:"args"`
+}
+
+// FunctionResponse represents the result of a tool execution.
+type FunctionResponse struct {
+	Name     string                 `json:"name"`
+	Response map[string]interface{} `json:"response"`
+}
+
+// GenerateContentRequest is the request payload for the streamGenerateContent endpoint.
+type GenerateContentRequest struct {
+	Contents         []Content         `json:"contents"`
+	Tools            []ToolDeclaration `json:"tools,omitempty"`
+	GenerationConfig `json:"generationConfig"`
+}
+
+// GenerationConfig defines model generation parameters.
+type GenerationConfig struct {
+	ThinkingConfig GenerationConfigThinkingConfig `json:"thinkingConfig,omitempty"`
+	Temperature    float64                        `json:"temperature,omitempty"`
+	TopP           float64                        `json:"topP,omitempty"`
+	TopK           float64                        `json:"topK,omitempty"`
+	// Temperature, TopP, TopK, etc. can be added here.
+}
+
+type GenerationConfigThinkingConfig struct {
+	IncludeThoughts bool `json:"include_thoughts,omitempty"`
+}
+
+// ToolDeclaration is the structure for declaring tools to the API.
+// For now, we'll assume a simple structure. A more complete implementation
+// would mirror the OpenAPI schema definition.
+type ToolDeclaration struct {
+	FunctionDeclarations []interface{} `json:"functionDeclarations"`
+}