feat: add AccountsModule with list and QR endpoints

Implements GET /accounts (list all accounts) and GET /accounts/:id/qr
(returns QR code as base64 data URL) using the qrcode package.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/api/package.json

@@ -18,6 +18,7 @@
     "@tower/logger": "workspace:*",
     "@tower/search": "workspace:*",
     "@tower/types": "workspace:*",
+    "qrcode": "^1.5.4",
     "reflect-metadata": "^0.2.0",
     "rxjs": "^7.8.0"
   },
@@ -27,6 +28,7 @@
     "@nestjs/testing": "^11.0.0",
     "@types/jest": "^29.0.0",
     "@types/node": "^22.0.0",
+    "@types/qrcode": "^1.5.6",
     "dotenv": "^17.4.2",
     "jest": "^29.0.0",
     "prisma": "^6.0.0",