feat: auth middleware, brain data layer, Valkey queue (P1-002/003/004) (#71)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.com>

apps/gateway/package.json

@@ -13,6 +13,8 @@
   },
   "dependencies": {
     "@mariozechner/pi-coding-agent": "~0.57.1",
+    "@mosaic/auth": "workspace:^",
+    "@mosaic/db": "workspace:^",
     "@nestjs/common": "^11.0.0",
     "@nestjs/core": "^11.0.0",
     "@nestjs/platform-fastify": "^11.0.0",
@@ -25,6 +27,7 @@
     "@opentelemetry/sdk-metrics": "^2.6.0",
     "@opentelemetry/sdk-node": "^0.213.0",
     "@opentelemetry/semantic-conventions": "^1.40.0",
+    "better-auth": "^1.5.5",
     "fastify": "^5.0.0",
     "reflect-metadata": "^0.2.0",
     "rxjs": "^7.8.0",