Clarify planning surfaces and retire stale milestone machinery

[flyingrobots]

Summary

Inventory and reconcile the repository's planning surfaces after the product clarification work.

Why

The repo currently has multiple competing control planes:

• open GitHub milestones that are all 100% complete relics
• open issues from older milestone eras (for example IRONCLAD / M9)
• local planning artifacts and docs that still encode the old platform/bridge roadmap
• newly rewritten product docs that frame git-mind as inference-first semantic repository intelligence

We need one coherent operating model.

Scope

• triage open GitHub issues against the new product frame
• close or retire stale GitHub milestones
• identify local manual tracking artifacts that should be aligned, archived, or demoted to historical notes
• decide whether backlog should be managed primarily via IBM Hills + Playbacks rather than GitHub milestones
• update design docs with the resulting operating model

Exit Criteria

• one recommended backlog operating model
• stale milestone machinery identified and retired or explicitly quarantined
• misaligned tracking/docs called out and reconciled
• product-facing docs no longer compete with historical planning surfaces

[flyingrobots]

Completed by the merged planning-surface cleanup and governance work in PRs #301 and #302. The repo now has a canonical docs hierarchy, Hills/Playbacks operating model, and ADR-backed planning governance.