Docs: packages/meta.json lists 'ai' and 'testing' pages that don't exist

Describe the bug

docs/content/docs/packages/meta.json includes "ai" and "testing" in its pages array, but neither ai.mdx/ai/ nor testing.mdx/testing/ exists under docs/content/docs/packages/ — so the AI package (which ships in the template as @repo/ai) has no documentation page at all, and both nav entries dangle.

Relatedly, the only AI documentation that does exist — docs/content/docs/examples/ai-chatbot.mdx — uses the AI SDK v4-era useChat API (input, handleInputChange) while the template ships ai@^6, so the example no longer matches the shipped package.

To Reproduce

1. grep -o '"ai"\|"testing"' docs/content/docs/packages/meta.json → both present
2. ls docs/content/docs/packages/ → no ai(.mdx), no testing(.mdx)

Expected behavior

Either the pages exist (an ai.mdx documenting @repo/ai, a testing.mdx documenting the vitest setup) or the entries are removed from meta.json.

Happy to PR either direction — authoring the missing ai.mdx + refreshing the chatbot example to AI SDK v6 seems the more useful fix.