feat(J): Phase J Self-Improvement Plugin — controlled improvement loop

- New self_improvement plugin: models, services, routes, plugin
- 4 SQLAlchemy models: ImprovementSignal, ImprovementPattern, ImprovementProposal, ImpactMeasurement
- Migration 0132: 4 tables with RLS
- Services: collect_signals, detect_patterns, create_proposal, evaluate_proposal, request_approval, activate_proposal, rollback_proposal, measure_impact
- 11 API routes under /api/v1/improvement/
- Frontend: improvement.ts API client, ImprovementPanel.tsx in AISidebar proactive tab
- 24/24 integration tests pass
- Fix: __init__.py imports Plugin class for discover_builtins() (self_improvement + knowledge)
- Fix: automation plugin register_plugin_contributions skips when no tenant exists

app/plugins/builtins/automation/plugin.py

@@ -248,7 +248,8 @@ class AutomationPlugin(BasePlugin):
             from sqlalchemy import select as sa_select
 
             # Get first tenant + admin user for seeding
-            from app.models.user import User, Tenant
+            from app.models.user import User
+            from app.models.tenant import Tenant
             tenant_result = await db.execute(sa_select(Tenant).limit(1))
             tenant = tenant_result.scalar_one_or_none()
             if tenant:
@@ -331,6 +332,9 @@ class AutomationPlugin(BasePlugin):
         tenant_result = await db.execute(select(Tenant).limit(1))
         tenant = tenant_result.scalar_one_or_none()
         default_tenant_id = tenant.id if tenant else None
+        if default_tenant_id is None:
+            logger.warning("No tenant found — skipping plugin contributions registration")
+            return
 
         # Register agent definitions
         agent_names: list[str] = []