dfa4982: Support Vercel Blob Signed URLs in the vercelBlob() adapter. In access: "private" mode, url() now mints a presigned GET scoped to the key that honors expiresIn (1 hour default, new defaultUrlExpiresIn option) instead of throwing, and capabilities.signedUrl.supported reports true, so the gateway redirects private downloads to storage instead of proxying them. signedUploadUrl() now returns a presigned PUT in either mode, with contentType and maxSize enforced by Vercel’s CDN; a positive minSize throws because Vercel has no minimum-size constraint. Requires @vercel/blob 2.4.0 or later, which is already the adapter’s peer range.