feat: microservices scaffold + Auth Service (Step 1)

- Add shared/ module: config, db, models, schemas, redis utilities
- Add Auth Service (services/auth/): register, login, refresh, me,
  ForwardAuth /verify endpoint for Traefik
- Add Traefik config: ACME/Cloudflare DNS-01, dynamic routing,
  ForwardAuth middleware, sticky sessions for WS Gateway
- Add service scaffolds: ws-gateway, chat, batch-agent, billing (READMEs)
- Add redis>=5.0.0 to requirements.txt
- Monolith app/ is untouched — strangler fig migration

services/auth/README.md

@@ -0,0 +1,16 @@
+# Auth Service
+
+Owns: user registration, login, JWT RS256 issuance, token refresh, `/me` endpoint.
+
+## Tables owned
+- `users`
+- `refresh_tokens`
+- `subscriptions` (read; Billing Service writes)
+
+## Endpoints
+- `POST /auth/register`
+- `POST /auth/login`
+- `POST /auth/refresh`
+- `GET /auth/me`
+- `PUT /auth/me`
+- `GET /auth/verify` (ForwardAuth for Traefik)