Retrospection conversation DM flow

[sunba91-su]

Goal

Implement conversational DM collection for team retrospectives, similar to standups but with retro-specific questions.

Acceptance Criteria

• New /retro command namespace:
  • /retro start - starts retro session for today
  • /retro add - adds to current column (DM walks through columns)
  • /retro submit - finishes and saves
  • /retro cancel - aborts
• DM conversation flow (reuse convstate):
  • Bot: "Starting retro. Column 1: What went well?"
  • User replies
  • Bot: "Column 2: What could be improved?"
  • ...repeat for each column
  • Bot confirms submission
• Permission: team member or lead
• Multi-team: --team flag
• Duplicate prevention: one retro per team per day

Technical Notes

• Add Type field to Conversation to distinguish standup vs retro
• Or create separate retro convstate manager
• Store items immediately (not just in-memory)

Dependencies

• Blocked by: Retrospection data model and store

[sunba91-su]

Blocked by: #28