chore: remove iFlow-related modules and dependencies

- Deleted `iflow` provider implementation, including thinking configuration (`apply.go`) and authentication modules.
- Removed iFlow-specific tests, executors, and helpers across SDK and internal components.
- Updated all references to exclude iFlow functionality.

internal/api/server.go

@@ -411,20 +411,6 @@ func (s *Server) setupRoutes() {
 		c.String(http.StatusOK, oauthCallbackSuccessHTML)
 	})
 
-	s.engine.GET("/iflow/callback", func(c *gin.Context) {
-		code := c.Query("code")
-		state := c.Query("state")
-		errStr := c.Query("error")
-		if errStr == "" {
-			errStr = c.Query("error_description")
-		}
-		if state != "" {
-			_, _ = managementHandlers.WriteOAuthCallbackFileForPendingSession(s.cfg.AuthDir, "iflow", state, code, errStr)
-		}
-		c.Header("Content-Type", "text/html; charset=utf-8")
-		c.String(http.StatusOK, oauthCallbackSuccessHTML)
-	})
-
 	s.engine.GET("/antigravity/callback", func(c *gin.Context) {
 		code := c.Query("code")
 		state := c.Query("state")
@@ -641,8 +627,6 @@ func (s *Server) registerManagementRoutes() {
 		mgmt.GET("/gemini-cli-auth-url", s.mgmt.RequestGeminiCLIToken)
 		mgmt.GET("/antigravity-auth-url", s.mgmt.RequestAntigravityToken)
 		mgmt.GET("/kimi-auth-url", s.mgmt.RequestKimiToken)
-		mgmt.GET("/iflow-auth-url", s.mgmt.RequestIFlowToken)
-		mgmt.POST("/iflow-auth-url", s.mgmt.RequestIFlowCookieToken)
 		mgmt.POST("/oauth-callback", s.mgmt.PostOAuthCallback)
 		mgmt.GET("/get-auth-status", s.mgmt.GetAuthStatus)
 	}