feat: container monitoring integration + polish (PR-3)

- Integration tests: SSE auth, connection limits, lifecycle hooks, event persistence (6 tests)
- Instance events history API: GET /instances/{id}/events
- Documentation updates: terminal.md, backend.md, frontend.md
- Performance: SSE max 5 connections, health monitor write-on-change

Quality gates: pytest 21 monitoring passed, 172 unit passed (4 pre-existing), vitest 14 passed, tsc clean, eslint clean, ruff clean

apps/api/src/api/tool_instances.py

@@ -2284,6 +2284,65 @@ async def check_instance_tunnel_health(
     return response
 
 
+@router.get(
+    "/{project_id}/repositories/{repo_id}/instances/{instance_id}/events",
+    summary="Get instance events history",
+    description="Get lifecycle event history for a tool instance.",
+)
+async def get_instance_events(
+    project_id: uuid.UUID,
+    repo_id: uuid.UUID,
+    instance_id: uuid.UUID,
+    limit: int = 50,
+    user_id: uuid.UUID = Depends(get_current_user_id),
+    session: AsyncSession = Depends(get_db_session),
+) -> list[dict]:
+    """Get lifecycle event history for an instance.
+
+    Args:
+        project_id: UUID of the project.
+        repo_id: UUID of the repository.
+        instance_id: UUID of the instance.
+        limit: Maximum number of events to return (default: 50).
+        user_id: ID of the authenticated user.
+        session: Database session.
+
+    Returns:
+        List of event dictionaries.
+    """
+    from sqlalchemy import select
+    from src.models.instance_event import InstanceEvent
+
+    _user = await _get_user(session, user_id)
+    _project = await _get_owned_project(project_id, user_id, session)
+
+    instance = await session.get(ToolInstance, instance_id)
+    if instance is None or instance.repository_id != repo_id:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND, detail="instance not found"
+        )
+
+    result = await session.execute(
+        select(InstanceEvent)
+        .where(InstanceEvent.instance_id == instance_id)
+        .order_by(InstanceEvent.created_at.desc())
+        .limit(limit)
+    )
+    rows = result.scalars().all()
+
+    return [
+        {
+            "id": str(row.id),
+            "event_type": row.event_type,
+            "status": row.status,
+            "message": row.message,
+            "metadata": row.event_metadata,
+            "created_at": row.created_at.isoformat() if row.created_at else None,
+        }
+        for row in rows
+    ]
+
+
 @router.get(
     "/{project_id}/repositories/{repo_id}/instances/{instance_id}/proxy/{path:path}",
     summary="Proxy to instance",