Add README and fix Dockerfile VITE build args

README covers all env vars, docker-compose/env examples, and full
auth server setup (scope, client registration, user roles).

Dockerfile now accepts VITE_AUTH_* build args with production defaults
so the values are baked into the client bundle correctly.

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

Dockerfile

@@ -4,6 +4,15 @@ WORKDIR /app/client
 COPY src/Budget.Client/package*.json ./
 RUN npm ci
 COPY src/Budget.Client/ ./
+
+ARG VITE_AUTH_AUTHORITY=https://auth.stwaddle.com/
+ARG VITE_AUTH_CLIENT_ID=budget-client
+ARG VITE_AUTH_REDIRECT_URI=https://budget.stwaddle.com/callback
+
+ENV VITE_AUTH_AUTHORITY=$VITE_AUTH_AUTHORITY
+ENV VITE_AUTH_CLIENT_ID=$VITE_AUTH_CLIENT_ID
+ENV VITE_AUTH_REDIRECT_URI=$VITE_AUTH_REDIRECT_URI
+
 RUN npm run build
 
 # Stage 2: Build and publish ASP.NET app