fix(pstack): correct grok model slug to cursor-grok-4.6-xhigh-fast

[ngurney]

Why

grok-4.6-fast-xhigh appears about 21 times as pstack's default fast-code model, but it matches no slug in cursor-agent --list-models. Out-of-the-box routing and setup-pstack defaults therefore point at a nonexistent model.

Scope

Replace that exact string under pstack/ with cursor-grok-4.6-xhigh-fast, which the CLI lists as Cursor Grok 4.6 Extra High Fast. No other model slug or content changes.

Tradeoffs

If the original slug is an intentional internal-only name, a maintainer should say so. This PR can instead document the public equivalent.

Blast Radius

This changes pstack's default model references only.

Verification

cursor-agent --list-models | rg '^(cursor-grok-4\.6-xhigh-fast|grok-4\.6-fast-xhigh) '

The command returns only cursor-grok-4.6-xhigh-fast - Cursor Grok 4.6 Extra High Fast.

Made with Cursor