Accept --memory 12GiB for the large GPU browser

[yummybomb]

Summary

kernel browsers create --gpu --memory 12GiB requests the large GPU browser tier (8 vCPU, 12 GiB memory, 4 GiB VRAM). browsers create --memory now accepts 12GiB alongside 8GiB and 16GiB, and the flag help says which values apply to CPU and GPU browsers.

browser-pools create and browser-pools update keep their own allowlist of 8GiB and 16GiB, since pools never run GPU browsers. --memory 12GiB on a pool now fails locally with invalid --memory value: 12GiB (must be one of 8GiB, 16GiB), matching the pool flag help.

For browsers create, the CLI only checks that the value is in the list. The API enforces the combination: 12GiB requires --gpu, and 8GiB/16GiB are CPU-only. Otherwise it returns a 400 with the reason, the same way --memory 16GiB --gpu is handled today.

The README's browsers create flag list now documents --gpu and --memory, which it did not list before.

Notes

• Depends on the API accepting memory=12GiB for GPU browsers. The Go SDK's BrowserMemoryRequest is a string type, so no SDK bump is needed to send the new value.

Testing

• go test ./... passes. New TestBrowserPoolsMemoryRejectsGPUTier covers pool create and update; TestBrowsersCreate_WithMemory covers 12GiB with --gpu.
• golangci-lint was not run (not installed locally).