refactor(backend): incremental architecture evolution (Task 19)

- Add common/ layer for shared capabilities (LLM, RAG, document, middleware)
- Add legacy/ layer for existing business code
- Move files to new structure (controllers, routes, services)
- Update index.ts for new route registration
- System remains fully functional

backend/package.json

@@ -11,8 +11,12 @@
     "prisma:generate": "prisma generate",
     "prisma:migrate": "prisma migrate dev",
     "prisma:studio": "prisma studio",
+    "prisma:seed": "tsx prisma/seed.ts",
     "test": "echo \"Error: no test specified\" && exit 1"
   },
+  "prisma": {
+    "seed": "tsx prisma/seed.ts"
+  },
   "keywords": [
     "ai",
     "clinical",
@@ -31,8 +35,12 @@
     "dotenv": "^17.2.3",
     "fastify": "^5.6.1",
     "form-data": "^4.0.4",
+    "html2canvas": "^1.4.1",
     "js-yaml": "^4.1.0",
+    "jspdf": "^3.0.3",
+    "p-queue": "^9.0.0",
     "prisma": "^6.17.0",
+    "tiktoken": "^1.0.22",
     "zod": "^4.1.12"
   },
   "devDependencies": {