build(deps): Bump ai and @mastra/core

Removes [ai](https://github.com/vercel/ai). It's no longer used after updating ancestor dependency [@mastra/core](https://github.com/mastra-ai/mastra/tree/HEAD/packages/core). These dependencies need to be updated together.


Removes `ai`

Updates `@mastra/core` from 0.10.0 to 1.21.0
- [Release notes](https://github.com/mastra-ai/mastra/releases)
- [Changelog](https://github.com/mastra-ai/mastra/blob/main/docs/CHANGELOG.md)
- [Commits](https://github.com/mastra-ai/mastra/commits/@mastra/core@1.21.0/packages/core)

---
updated-dependencies:
- dependency-name: ai
  dependency-version: 
  dependency-type: indirect
- dependency-name: "@mastra/core"
  dependency-version: 1.21.0
  dependency-type: direct:development
...

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Author: dependabot[bot]