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-stale-task-mtime-proxy/BUG_REPORT.md

@@ -1,13 +0,0 @@
-# Bug Report: fix-stale-task-mtime-proxy
-
-## Scope
-Reviewed `scripts/status.py` `_get_edit_timestamp()`, `_touch_lastedit()`, `cmd_can_edit()`, `cmd_same_session()`, `cmd_touch()`.
-
-## Findings
-No bugs found. The `.state.lastedit` mechanism correctly:
-- Is touched on ALLOWED `--can-edit` responses
-- Falls back to `.state` mtime when `.state.lastedit` doesn't exist
-- Is excluded from `NON_ARTIFACT_FILES`
-- Used consistently across `--can-edit`, `--same-session`, and `--touch`
-
-## Verdict: PASS