Rework client OIDC env vars: rename to VITE_OIDC_*, add committed .env

Renames VITE_AUTH_* to VITE_OIDC_* to match the stack convention.
Adds a dedicated VITE_OIDC_POST_LOGOUT_REDIRECT_URI instead of deriving
it from the redirect URI via string replace. Switches from Dockerfile
ARG/ENV to a committed src/Budget.Client/.env so Vite picks up
production values at build time without needing build-arg overrides.
.env.local is gitignored for localhost dev overrides.

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

Dockerfile

@@ -5,14 +5,6 @@ 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