Support 100 MB notebook source uploads

[suguanYang]

Summary

• Route large source uploads through private Vercel Blob client uploads so the browser no longer posts >4.5 MB files directly to /api/sources.
• Add /api/source-uploads/blob to issue authenticated Blob client-upload tokens capped at the existing 100 MB document limit.
• Let /api/sources accept Blob metadata, stream the private staged Blob into a temp file for Knowhere upload, and delete the staging Blob afterward.
• Keep the existing small-file multipart path unchanged.

Verification

• Red/green pnpm test src/lib/source-upload-request.test.ts -- --runInBand
• Red/green pnpm test src/app/api/sources/route.test.ts -- --runInBand
• Red/green pnpm test src/app/api/source-uploads/blob/route.test.ts -- --runInBand
• Red/green pnpm test src/lib/source-upload.test.ts -- --runInBand
• pnpm test
• pnpm exec tsc --noEmit
• pnpm lint
• pnpm build
• git diff --check

Notes

The staging failure was FUNCTION_PAYLOAD_TOO_LARGE, which happens before our route code can handle a large multipart body. This PR avoids that platform limit by sending large files from the browser to Vercel Blob first, then sending only a small metadata payload to the app route.

[vercel]

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Project	Deployment	Actions	Updated (UTC)
knowhere-notebook-staging	Ready	Preview, Comment	May 10, 2026 8:59am