Replace Zod with TypeBox for schema validation

- Switch from Zod to TypeBox for tool parameter schemas
- TypeBox schemas can be serialized/deserialized as JSON
- Use AJV for runtime validation instead of Zod's parse
- Add StringEnum helper for Google API compatibility (avoids anyOf/const patterns)
- Export Type and Static from main package for convenience
- Update all tests and documentation to reflect TypeBox usage

packages/ai/src/providers/openai-completions.ts

@@ -7,7 +7,6 @@ import type {
 	ChatCompletionContentPartText,
 	ChatCompletionMessageParam,
 } from "openai/resources/chat/completions.js";
-import { zodToJsonSchema } from "zod-to-json-schema";
 import { AssistantMessageEventStream } from "../event-stream.js";
 import { calculateCost } from "../models.js";
 import type {
@@ -396,7 +395,7 @@ function convertTools(tools: Tool[]): OpenAI.Chat.Completions.ChatCompletionTool
 		function: {
 			name: tool.name,
 			description: tool.description,
-			parameters: zodToJsonSchema(tool.parameters, { $refStrategy: "none" }),
+			parameters: tool.parameters as any, // TypeBox already generates JSON Schema
 		},
 	}));
 }