/dashboard

Display task progress dashboard with status counts, completion percentage, and recent activity

# Tasks Dashboard Command

You are implementing `/mwguerra:taskmanager:dashboard`.

## Behavior

1. Ask the `taskmanager` skill to:
   - Read `.taskmanager/tasks.json`.
   - Flatten all tasks and subtasks into a single list.
   - Ensure `estimateSeconds` is populated for all leaf tasks and rollups are recomputed for parents (see the skill’s estimation rules).
   - Ensure `status` propagation is up to date for all parents.

2. Compute summary metrics such as:
   - Total number of tasks (all levels).
   - Number of leaf tasks vs parent tasks.
   - Counts by `status` (`planned`, `in-progress`,...