PR shepherd: route agent PRs to the right human reviewer via code ownership #414

From the Sentry Seer research: their dogfood showed the bottleneck is human review, not fix generation. Their fix was an hourly routine that picks a reviewer from git blame/commit history against the RCA'd files and pings them, with politeness rules learned over two weeks (no weekend pings, no double-posts, skip closed PRs) — +21% action rate.

For Solenta: an automation that watches agent-produced PRs, computes the right reviewer from code ownership, and nudges them — closing the last mile between agent output and human attention. Pairs with #260 (agent-PR triage inbox).