Add both pull_request and pull_request_target triggers to support:
- pull_request: Same-repo PRs (works immediately with changed workflow)
- pull_request_target: Fork PRs (provides OIDC tokens)
This resolves the chicken-and-egg problem where pull_request_target
uses the base branch's workflow file, preventing the workflow from
running when the workflow file itself is changed in the PR.
Switch from pull_request to pull_request_target event to enable
OIDC token access for external contributor PRs. This allows the
Claude Code action to authenticate properly when reviewing PRs
from forks.
Also added explicit PR head SHA ref to checkout to ensure we
review the correct code.
Fixes workflow failure: Unable to get ACTIONS_ID_TOKEN_REQUEST_URL
