fix(executor): remove unused import and vertex variable

Drop an unused fmt import in BaseExecutor and ignore an unused projectID value in Gemini Vertex provider credentials path to satisfy Go compiler checks.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/runtime/executor/base_executor.go

@@ -4,7 +4,6 @@ import (
 	"bufio"
 	"bytes"
 	"context"
-	"fmt"
 	"io"
 	"net/http"
 

internal/runtime/executor/gemini_vertex_provider.go

@@ -42,7 +42,7 @@ func (p *GeminiVertexProvider) GetCredentials(auth *cliproxyauth.Auth) (apiKey,
 	}
 
 	// Fall back to service account - return empty apiKey to signal service account auth
-	projectID, location, _, err := vertexCreds(auth)
+	_, location, _, err := vertexCreds(auth)
 	if err != nil {
 		return "", ""
 	}