Formalize Post-PR Mini Retro procedure in knowledge/procedures

## Current State

The detailed Post-PR Mini Retro procedure currently lives in the global CLAUDE.local.md file but hasn't been formalized in the knowledge/procedures directory. The current `post-pr-mini-retro.md` file is just a 3-line stub that references the continuous improvement principle.

## Problem

- The detailed retro questions and agent-led collaborative process are not in a formal procedure file
- The `/retro` command only injects `continuous-improvement.md`, missing the detailed questions
- This violates the single source of truth principle

## Proposed Solution

1. **Create comprehensive post-pr-mini-retro.md** in knowledge/procedures/
- Copy the detailed content from CLAUDE.local.md
- Include all retro questions:
- What worked well?
- What didn't work as expected?
- Procedure adherence
- Systems improvement opportunities
- Formatting overhead check
- Tool boundary clarity
- Principle tensions
- Include the agent-led collaborative process section
- Include personality-driven focus (Jonah, Brent, etc.)

2. **Update the retro command template** to inject the full procedure:
```markdown
{{ INJECT:procedures/post-pr-mini-retro.md }}
```

3. **Consider relationship between**:
- `/retro` command (general retrospective)
- Post-PR specific retro procedure
- Continuous improvement principle

## Benefits

- Single source of truth for retro procedures
- Agents can access detailed retro questions via INJECT pattern
- Follows systems-stewardship principle
- Enables consistent retro experiences

## Related

- PR #1097 discovered this gap
- Implements systems-stewardship principle
- Part of making procedures AI-actionable

Start with knowledge/procedures/post-pr-mini-retro.md and compare its stub with the detailed procedure in CLAUDE.local.md. Then locate the retro command template and update it to inject procedures/post-pr-mini-retro.md; done means the procedure contains the listed questions and collaborative-process details, and /retro receives the full procedure.

Written by the indexing model from the issue text.