chore: import upstream snapshot with attribution

Sources/CodexBar/Providers/VertexAI/VertexAIProviderImplementation.swift

@@ -0,0 +1,13 @@
+import CodexBarCore
+import Foundation
+
+struct VertexAIProviderImplementation: ProviderImplementation {
+    let id: UsageProvider = .vertexai
+    let supportsLoginFlow: Bool = true
+
+    @MainActor
+    func runLoginFlow(context: ProviderLoginContext) async -> Bool {
+        await context.controller.runVertexAILoginFlow()
+        return false
+    }
+}