Update PRCommentWorkflow to use PhaseOps I/O methods

[devloop-bot]

Parent

Parent: #196

What to build

Remove _WorkflowCommon from PRCommentWorkflow inheritance and migrate all I/O calls to use PhaseOps methods. PRCommentWorkflow should inherit only PhaseOps.

PRCommentWorkflow uses the same _WorkflowCommon pattern as DevLoopWorkflow. Removing the _WorkflowCommon inheritance and consolidating onto PhaseOps closes the second instance of the parallel I/O protocol.

Acceptance criteria

• PRCommentWorkflow inherits only from PhaseOps (not _WorkflowCommon)
• All _comment, _dispatch, _cleanup, _request_reviewer, _emit_kpis calls use PhaseOps methods
• PRCommentWorkflow code paths exercise the new PhaseOps methods end-to-end
• All existing tests still pass
• PR comment workflow still functions correctly

Blocked by

• Merge _WorkflowCommon I/O methods into PhaseOps #197 (Merge _WorkflowCommon I/O methods into PhaseOps)