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/self_improvement/plugin.py

@@ -0,0 +1,46 @@
+"""Self-improvement plugin — controlled improvement loop.
+
+Builds on existing systems:
+- ai_proactive: ContextLog, ProactiveSuggestion (signals)
+- automation: AgentRun, AgentVersion (versioning + runs)
+- app.core.approval: ApprovalRequest (human approval)
+- app.ai.oversight: DecisionRecord (audit trail)
+- app.ai.llm_client: llm_complete (evaluation)
+- AuditLog, WorkflowInstance (usage data)
+"""
+from __future__ import annotations
+
+import logging
+
+from app.plugins.base import BasePlugin
+from app.plugins.manifest import PluginManifest, PluginRouteDef
+
+logger = logging.getLogger(__name__)
+
+
+class SelfImprovementPlugin(BasePlugin):
+    manifest = PluginManifest(
+        name="self_improvement",
+        version="1.0.0",
+        display_name="Self-Improvement",
+        description="Controlled self-improvement loop: signals, patterns, proposals, evaluation, approval, activation, rollback, impact measurement.",
+        dependencies=["permissions", "automation", "ai_proactive"],
+        routes=[
+            PluginRouteDef(
+                path="/api/v1/improvement",
+                module="app.plugins.builtins.self_improvement.routes",
+                router_attr="router",
+            ),
+        ],
+        permissions=["improvement:read", "improvement:write", "improvement:admin"],
+    )
+
+    async def on_activate(self, db, service_container, event_bus) -> None:
+        """Register self-improvement hooks on activation."""
+        await super().on_activate(db, service_container, event_bus)
+        logger.info("Self-improvement plugin activated")
+
+    async def on_deactivate(self, db, service_container, event_bus) -> None:
+        """Clean up on deactivation."""
+        await super().on_deactivate(db, service_container, event_bus)
+        logger.info("Self-improvement plugin deactivated")