fix: expose custom fetch on typed Tinybird client

[rmorehig]

Summary

• expose fetch on the typed Tinybird constructor and pass it into client bootstrap
• use the custom fetch for preview token resolution and branch-management requests so typed clients behave consistently end to end
• add regression coverage for typed queries, preview/dev-mode resolution, and document the Next.js cache: "no-store" pattern

Testing

• corepack pnpm typecheck
• corepack pnpm vitest run src/schema/project.test.ts src/client/preview.test.ts src/api/branches.test.ts src/client/base.test.ts src/client/tokens.test.ts
• corepack pnpm test:run

Closes #128