feat: Allow using Gemini Web without login

- Remove requirement to login before using Gemini Web
- If logged in (cookies exist), use the account
- If not logged in, continue without login (browser opens)
- When browser is visible, prompt user they can login or continue without
- Save cookies only if user actually logs in

internal/providers/geminiweb/provider.go

@@ -49,17 +49,31 @@ func (p *Provider) Generate(ctx context.Context, model string, messages []apityp
 		return err
 	}
 
+	// 檢查是否有可用的已登入 session
 	session := p.pool.GetAvailable()
-	if session == nil {
-		return fmt.Errorf("no available sessions - please run 'gemini-login <session-name>' first")
-	}
+	needLogin := false
 
-	fmt.Printf("[GeminiWeb] Using session: %s\n", session.Name)
+	if session == nil {
+		// 沒有 session，建立一個新的
+		fmt.Printf("[GeminiWeb] No existing session found, creating new session...\n")
+		var err error
+		session, err = p.pool.CreateSession(fmt.Sprintf("session-%d", time.Now().Unix()))
+		if err != nil {
+			return fmt.Errorf("failed to create session: %w", err)
+		}
+		needLogin = true
+		fmt.Printf("[GeminiWeb] Created new session: %s\n", session.Name)
+	} else {
+		fmt.Printf("[GeminiWeb] Using existing session: %s\n", session.Name)
+	}
 
 	p.pool.StartSession(session)
 	defer p.pool.EndSession(session)
 
-	browser, err := NewBrowser(p.cfg.GeminiBrowserVisible)
+	// 如果沒有登入過，強制使用可見瀏覽器
+	visible := p.cfg.GeminiBrowserVisible || needLogin
+
+	browser, err := NewBrowser(visible)
 	if err != nil {
 		return fmt.Errorf("failed to create browser: %w", err)
 	}
@@ -70,16 +84,18 @@ func (p *Provider) Generate(ctx context.Context, model string, messages []apityp
 		return fmt.Errorf("failed to create page: %w", err)
 	}
 
+	// 嘗試載入 cookies
 	if session.CookieFile != "" {
 		fmt.Printf("[GeminiWeb] Loading cookies from: %s\n", session.CookieFile)
 		cookies, err := LoadCookiesFromFile(session.CookieFile)
 		if err == nil {
 			if err := SetCookiesOnPage(page, cookies); err != nil {
-				return fmt.Errorf("failed to set cookies: %w", err)
-			}
-			fmt.Printf("[GeminiWeb] Loaded %d cookies\n", len(cookies))
+				fmt.Printf("[GeminiWeb] Warning: failed to set cookies: %v\n", err)
 			} else {
-			fmt.Printf("[GeminiWeb] Warning: could not load cookies: %v\n", err)
+				fmt.Printf("[GeminiWeb] Loaded %d cookies\n", len(cookies))
+			}
+		} else {
+			fmt.Printf("[GeminiWeb] No existing cookies found\n")
 		}
 	}
 
@@ -91,10 +107,42 @@ func (p *Provider) Generate(ctx context.Context, model string, messages []apityp
 	time.Sleep(2 * time.Second)
 
 	fmt.Printf("[GeminiWeb] Checking login status...\n")
-	if !IsLoggedIn(page) {
-		return fmt.Errorf("session not logged in - please run 'gemini-login %s' first", session.Name)
+	if IsLoggedIn(page) {
+		fmt.Printf("[GeminiWeb] Logged in (using saved cookies)\n")
+	} else {
+		fmt.Printf("[GeminiWeb] Not logged in - continuing without login\n")
+
+		if visible {
+			// 開啟可見瀏覽器，提示使用者可以登入
+			fmt.Println("\n========================================")
+			fmt.Println("Browser is now open. You can:")
+			fmt.Println("1. Log in to Gemini (to use your account)")
+			fmt.Println("2. Or continue without login (limited functionality)")
+			fmt.Println("\nPress Enter when ready to continue...")
+			fmt.Println("========================================\n")
+
+			// 等待使用者按 Enter
+			var input string
+			fmt.Scanln(&input)
+
+			// 檢查是否已登入
+			if IsLoggedIn(page) {
+				fmt.Printf("[GeminiWeb] Login detected! Saving cookies for future use...\n")
+				cookies, err := GetPageCookies(page)
+				if err != nil {
+					fmt.Printf("[GeminiWeb] Warning: could not get cookies: %v\n", err)
+				} else {
+					if err := SaveCookiesToFile(cookies, session.CookieFile); err != nil {
+						fmt.Printf("[GeminiWeb] Warning: could not save cookies: %v\n", err)
+					} else {
+						fmt.Printf("[GeminiWeb] Saved %d cookies to %s\n", len(cookies), session.CookieFile)
+					}
+				}
+			} else {
+				fmt.Printf("[GeminiWeb] Continuing without login\n")
+			}
+		}
 	}
-	fmt.Printf("[GeminiWeb] Logged in successfully\n")
 
 	fmt.Printf("[GeminiWeb] Selecting model: %s\n", model)
 	if err := SelectModel(page, model); err != nil {