Add framework design docs (model-divergence, rule agents, agent tab)

Design docs in design/framework/ covering:
- Model-divergence enforcement (conflict matrix, modes, auto-assignment)
- Rule Proposer agent (daily scan, proposes rules to RULE_PROPOSALS.md)
- Rule Reviewer agent (monthly consolidation, different LLM than Proposer)
- Agent tab redesign (phase roles + scheduled jobs, remove fake types)
- Schedules, conflict-of-interest, success criteria

Cross-references updated in AGENTS.md, README.md, CHANGELOG.md,
.onboarding.md, prompts/onboarding.md, design/loops/{README,BACKLOG}.md,
memory/v1-1-hardening-session.md.

Also restores scripts/automaton-cleanup.sh stub (was corrupted by
pytest test leak writing temp path into real stub).

.onboarding.md

@@ -111,3 +111,12 @@ When the agent receives a trigger command, it must:
 1. Read the corresponding template file.
 2. Replace all `{placeholders}` with the actual project values.
 3. Execute the rendered prompt.
+
+## Backlog
+
+Design backlogs are the framework's outstanding-work store when no active tasks exist. Each design area has its own `BACKLOG.md`:
+
+- `~/.automaton/design/loops/BACKLOG.md` — loop engineering v1.1+ and deferred items.
+- `~/.automaton/design/framework/BACKLOG.md` — framework-level agent features (rule agents, Agent tab redesign, model-divergence enforcement).
+
+The self-improvement loop consumes these automatically when configured with `work_source.kind = "backlog"` and `work_source.area` set to the relevant design area (`"loops"` or `"framework"`). For manual work, read the topmost `- [ ]` item and create a task via `status.py --create-task`.