Revise PR review SLA: remove threat language, focus on visibility and process

Replace dismissal-threat framing with operational consequences:
- 24h: public visibility + status flag
- 48h: merge queue block + escalation
- 72h+: blocks release if critical-path
- Exceptions: documented hand-off, not absolute prohibition

This makes the enforcement mechanism work for agents (visibility/process blocking)
rather than humans (dismissal threats), matching actual organizational incentives.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

null-pointer-nancy/test.txt

@@ -0,0 +1 @@
+test