chore: Remove mastra in favor of ai sdk v5 (#1356)

[tlgimenes]

Remove mastra. Drastically improve bundle sizes and improve overall cloudflare performance. Still using mastra memory, but I plan on ditching them soon. Went from 18Mb to 9Mb.

Summary by CodeRabbit

• New Features

  • Supabase-backed knowledge base for faster, more reliable vector search.
  • Enhanced voice features: improved transcription and speech generation.
  • Chat API now supports sendMessage with richer UI state.

• Improvements

  • Chat experience: better attachments, image rendering, tool-call displays, retry flow, and finish-reason handling.
  • Email ingestion uses MIME parsing for cleaner text/HTML.
  • More reliable thread history, titles, and metadata.

• Chores

  • Major dependency upgrades (AI SDK v5, React 19.2) and Node >= 24 requirement.
  • Removed legacy memory UI controls; simplified Advanced settings.
  • Incremental TypeScript builds, VS Code TS SDK config, and updated ignore rules.