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/fix-dashboard-read-state/BUG_REPORT.md

@@ -1,9 +0,0 @@
-# Bug Report: fix-dashboard-read-state
-
-## Scope
-Reviewed `automaton/dashboard/core/task.py` `_state_string_to_task_state()` and `determine_task_state()`.
-
-## Findings
-No bugs found. The `.state` file is correctly read and takes precedence over artifact heuristic. Sub-state handling (split on `:`) is correct. Fallback to artifacts for tasks without `.state` is maintained.
-
-## Verdict: PASS