feat(ai): Implement Zod-based tool validation and improve Agent API

- Replace JSON Schema with Zod schemas for tool parameter definitions
- Add runtime validation for all tool calls at provider level
- Create shared validation module with detailed error formatting
- Update Agent API with comprehensive event system
- Add agent tests with calculator tool for multi-turn execution
- Add abort test to verify proper handling of aborted requests
- Update documentation with detailed event flow examples
- Rename generate.ts to stream.ts for clarity

packages/ai/src/index.ts

@@ -1,8 +1,9 @@
+export { z } from "zod";
 export * from "./agent/index.js";
-export * from "./generate.js";
 export * from "./models.js";
 export * from "./providers/anthropic.js";
 export * from "./providers/google.js";
 export * from "./providers/openai-completions.js";
 export * from "./providers/openai-responses.js";
+export * from "./stream.js";
 export * from "./types.js";