fix(site): add missing OG image for /compute page (#7940)

* fix(site): add missing OG image for /compute page

The compute page metadata references /og/og-compute.png, but the file
was never committed, so the OG image 404s in production. Serve it from
a route handler that renders the image at build time, and extract the
OG template shared with the blog OG route into src/lib/og-image.tsx.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(site): use Compute public beta blog OG image for /compute

Replace the generated OG route with the designed meta image from the
launching-prisma-compute-public-beta blog post, served as a static
file from public/og/ like the other product pages.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

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Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: ankur-arch