feat: add retrospective intelligence to create-story workflow

Load all retrospective files during story creation to carry forward
lessons learned, open action items, architecture corrections, and
deferred code review items. Fulfills Epic 2 retro action item A1.

Also includes Epic 2 retrospective and sprint status updates.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

_bmad/bmm/workflows/4-implementation/create-story/template.md

@@ -21,6 +21,13 @@ so that {{benefit}}.
 - [ ] Task 2 (AC: #)
   - [ ] Subtask 2.1
 
+## Retrospective Intelligence
+
+- Applicable lessons from previous epics
+- Open action items affecting this story
+- Architecture corrections to incorporate
+- Deferred code review items relevant here
+
 ## Dev Notes
 
 - Relevant architecture patterns and constraints