Updates the compute private beta page with the May 1 release entry, plus
a deploy-time warning when `us-east-1-next` is the project default.
The new What's new entry, verbatim:
### May 1, 2026
- **Cold starts are faster across all machine sizes.** Every preset
starts faster, including `micro` and `small-1x` - there's no longer a
cold-start penalty for picking a smaller machine.
- **First runs after a deploy are faster on every preset.** Boot
snapshot creation is significantly quicker across the board, so the cold
path is consistently snappier.
- **`large-1x` and `large-2x` no longer hard-fail.** They're still not
recommended - cold-start performance trails the smaller presets and
we're ironing out reliability issues.
Follow-up to #3472 and #3479.
nicktrn