security: harden PR review workflow triggers and checkout

[enyst]

Summary

• require explicit maintainer action before the PR review workflow runs
• review fork PRs from a trusted base checkout while sourcing the diff from the GitHub API
• default the workflow template to the ephemeral github.token
• update PR review docs/tests to match the hardened behavior

Why

This is the remaining worthwhile follow-up from the closed OpenHands/software-agent-sdk#2119 investigation. The software-agent-sdk side was largely superseded, but the migrated PR-review workflow/plugin now lives in OpenHands/extensions, where the privileged pull_request_target flow still needed hardening.

The setup-uv cache hardening was split into #159 so it can be reviewed and merged independently.

Testing

• uv run --with pytest pytest tests/test_pr_review_review_context.py tests/test_workflow_sync.py
• git diff --check

This PR was created by an AI assistant (OpenHands) on behalf of the user.

@enyst can click here to continue refining the PR

[enyst]

@OpenHands Separate the cache fix in another PR from main. Mark it ready for review and babysit until an AI reviewer agent comments; address its inline feedback if any. If it approves it, merge it. Then post a comment here tagging me, so that I know.

[enyst]

@enyst Done — I split the cache change into #159, marked it ready for review, waited for the AI reviewer, and it approved with no inline feedback to address. I then merged #159.

PR #158 is now updated to exclude the cache change and references #159 in the description.

This comment was created by an AI assistant (OpenHands) on behalf of the user.

[enyst]

Merged main into this branch and fixed the conflict. The overlap came from #159 landing on main while this PR was still editing the same PR-review security docs/files, so I kept both pieces: main's cache-hardening note and this PR's trigger/checkout/github.token changes.

Re-ran: uv run --with pytest pytest tests/test_pr_review_review_context.py tests/test_workflow_sync.py and git diff --check.

This comment was created by an AI assistant (OpenHands) on behalf of the user.