feat(orchestrator): add MS23 per-agent message history and SSE stream endpoints

GET /agents/:id/messages - paginated message history
GET /agents/:id/messages/stream - SSE live stream with replay

Partial #693

apps/orchestrator/package.json

@@ -7,7 +7,7 @@
     "dev": "nest start --watch",
     "lint": "eslint src/",
     "lint:fix": "eslint src/ --fix",
-    "prisma:generate": "prisma generate --schema=./prisma/schema.prisma",
+    "prisma:generate": "prisma generate --schema=../api/prisma/schema.prisma",
     "start": "node dist/main.js",
     "start:debug": "nest start --debug --watch",
     "start:dev": "nest start --watch",