Enhanced plan dashboard with progress and milestone scoping

Acceptance Criteria

• Dashboard shows a progress summary line per entity type (e.g., "35 work items: 12 done, 3 in progress, 7 ready, 2 blocked, 11 draft")
• Status counts are color-coded using the existing status palette
• Blocked items section with warning styling surfaces all status: blocked entities
• When multiple milestones exist, work items and bugs are grouped by milestone with per-milestone progress
• When one or zero milestones exist, flat layout is used (current behavior)
• Recent activity section shows last 10 items by file modification time
• Existing dashboard sections (active milestone, ready, in-progress, recent decisions) are preserved

Approach

Extend the dashboard generation in @refrakt-md/plan's aggregate pipeline phase. Progress summaries and milestone grouping are computed from the entity registry. Recent activity uses mtime from the file scanner.

Note: The dashboard page uses generateDashboardContent() which produces Markdoc content, not raw HTML. This approach is independent of WORK-050's renderer convergence — the dashboard generation creates content that flows through whatever renderer is active.

References

• Plan Site UX at Scale (Plan Site UX at Scale — Feature 3)
• Refactor plan render pipeline to use @refrakt-md/html (HTML adapter refactor — prerequisite)