Milestone Auto-Backlog and Checklist Progress

Summary

Two related rendering enhancements for the plan package:

1. Milestone auto-backlog: The milestone rune automatically appends a filtered view of all work items and bugs assigned to its name, grouped by status. This makes milestones self-updating — as work items are created with milestone="v0.5.0", they appear in the v0.5.0 milestone page automatically.

2. Checklist progress: Work items with - [ ] / - [x] checkbox lists show a progress indicator in their header (e.g., 2/5 or a progress bar). The milestone view shows aggregate progress across all assigned items.

Acceptance Criteria

• Milestone postProcess hook queries entity registry for work/bug entities with matching milestone field
• Queried items rendered as summary cards below the milestone's own content
• Items grouped by status (done, in-progress, ready, etc.)
• Work items with checkbox lists show checked/total count in header
• Milestone shows aggregate progress (total checked / total checkboxes across all items)
• CSS for progress indicator (bar or fraction display)
• Tests for milestone query, progress counting, and rendering

Approach

Checklist progress likely uses a postTransform hook on the work rune config that walks the renderable tree counting checkbox list items. The count is injected as a data attribute or structural element.

Milestone auto-backlog uses a postProcess pipeline hook that queries the entity registry and appends backlog card markup to the milestone's renderable tree.

Dependencies

• Add Entity Registration to @refrakt-md/plan (entity registration) — entities must be registered first
• Build backlog Rune (backlog rune) — card layout rendering can be shared