chore(ci): bump Node 20 actions to Node 24 runtime

[zfarrell]

Bumps GitHub Actions in claude-pr-review.yml from Node 20 to Node 24 runtimes.

• actions/checkout: v4 -> v6.0.2
• actions/create-github-app-token: v2 -> v3.2.0

Breaking changes to review:

• actions/checkout v4->v6: dropped Node20 for Node24 runtime; v5 updated default ref/checkout behavior and bumped minimum runner; verify any reliance on older glibc/runner images.
• actions/create-github-app-token v2->v3: runtime moved to Node24; v3 changed default owner/permissions handling - confirm owner input still set explicitly (it is here).