Archive completed tasks, add cleanup commands, self-documenting dashboard UI

- Archive 79 completed framework-dev tasks from tasks/ -> tasks/complete/
- status.py: add --cleanup-done and --install-cleanup-schedule commands
- Add scripts/automaton-cleanup.sh for periodic task archiving
- Dashboard: rename 'Background' tab -> 'Agent', 'Cleanup' agent -> 'Completed Task Archiver', remove redundant group headers and pill badges, dim inactive agent placeholders
- .rules.md: add Self-Documenting UI Names rule
- New tests: test_cleanup_done.py, expanded test_app.py and test_task.py

tasks/complete/task-status-reason/IMPLEMENTATION.md

@@ -0,0 +1,17 @@
+# Implementation: Add Status Reason to Task Display
+
+## Summary
+Added `status_reason` property to `Task` model providing human-readable explanations for each task state, exposed it in API responses, displayed it prominently in the detail panel and on task cards. Fixed the pending review count to exclude terminal-state tasks. Replaced approve/request-changes buttons with revoke buttons when a review is already submitted.
+
+## Changes
+- `automaton/dashboard/core/task.py`: Added `status_reason` property on `Task` with explanations for all 10+ task states
+- `automaton/dashboard/ui/app.py`: Added `status_reason` to `_serve_tasks()` and `_serve_task()` JSON responses; accepted `"pending"` as valid review status
+- `automaton/dashboard/html/dashboard.js`: Displayed `status_reason` in detail panel and on task cards; fixed pending count to exclude done/blocked; added conditional button rendering for approved/changes_requested reviews
+- `automaton/dashboard/html/styles.css`: Added `.detail-status-reason` and `.task-card-reason` styles
+- `tests/test_task.py`: Added `TestStatusReason` class with 5 tests covering done, blocked, and in-progress states
+
+## Test Results
+156 passed
+
+## Blockers
+None