chore: disable automatic PR review trigger

[jesseturner21]

Summary

• Comments out the pull_request trigger on the AI review workflow so it no longer runs automatically on PR open/reopen
• The workflow can still be triggered manually via workflow_dispatch

Test plan

• Verify the workflow no longer triggers on PR open/reopen
• Verify manual workflow_dispatch still works

[jesseturner21]

This PR doesn't actually achieve its stated goal — it's effectively a no-op after merging.

The branch was created from a commit before #958 merged to main. PR #958 changed the workflow trigger from pull_request to pull_request_target (for fork PR support). This PR's diff comments out pull_request:, but on current main that line doesn't exist — it's pull_request_target: instead.

I verified this by merging the branch locally: git diff origin/main against the merge result returns empty, so merging this PR would leave pull_request_target: still active and the workflow would keep auto-triggering on PR open/reopen.

To actually disable the automatic trigger, you'll need to rebase onto current main and comment out (or remove) the pull_request_target: block instead:

on:
  # pull_request_target:
  #   types: [opened, reopened]
  workflow_dispatch:
    ...