Add lightweight retrospective/feedback loop pattern

[loehnertz]

Description

The framework covers the journey from problem to implementation-ready tickets (Discover → Design → Decide → Decompose), but there's no guidance for closing the feedback loop after implementation. Did the work achieve its goals? What did we learn?

Problem

Without a retrospective pattern:

• We don't systematically capture whether decisions worked out
• Learnings from implementation stay in people's heads
• Future initiatives can't benefit from past outcomes
• "Superseding" a decision happens reactively rather than through deliberate evaluation

Suggested Approach

Add a lightweight retrospective artifact or section that captures:

• Outcome: Did the implementation achieve the initiative's goal?
• Learnings: What surprised us? What would we do differently?
• Decision validation: Were the trade-offs we accepted the right ones?
• Follow-up: Any new initiatives spawned from this work?

This could be:

1. A new artifact type (Retrospective.md) in the initiative folder
2. A "Retrospective" section added to Decision.md after implementation
3. A status update in the initiative's AGENTS.md

The key is keeping it lightweight – a few bullet points, not a formal post-mortem document. The goal is to close the loop, not add bureaucracy.

Open Questions

• Should this be opt-in or a recommended practice for all initiatives?
• How does this interact with the archive/completion pattern (Add archive/completion pattern for initiatives #3)?
• Should there be a /forge-retrospective command to prompt this?