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

frontend/src/components/layout/AISidebar.tsx

@@ -2,6 +2,7 @@ import React, { useState, useEffect } from 'react';
 import { ChatWindow } from '@/components/ai/ChatWindow';
 import { ResizablePanel } from '@/components/ui/ResizablePanel';
 import { SuggestionList } from '@/components/ai/SuggestionSidebar';
+import { ImprovementPanel } from '@/components/ai/ImprovementPanel';
 import { createSession, fetchSessions } from '@/api/ai';
 import { useUIStore } from '@/store/uiStore';
 import { useTranslation } from 'react-i18next';
@@ -172,7 +173,14 @@ export function AISidebar() {
 
   const renderTabContent = () => {
     if (aiSidebarTab === 'proactive') {
-      return <SuggestionList />;
+      return (
+        <div className="flex flex-col h-full">
+          <SuggestionList />
+          <div className="border-t border-secondary-200">
+            <ImprovementPanel />
+          </div>
+        </div>
+      );
     }
     if (aiSidebarTab === 'notifications') {
       return (