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>

src/Budget.Client/.env

@@ -0,0 +1,4 @@
+VITE_OIDC_AUTHORITY=https://auth.stwaddle.com
+VITE_OIDC_CLIENT_ID=budget-client
+VITE_OIDC_REDIRECT_URI=https://budget.stwaddle.com/callback
+VITE_OIDC_POST_LOGOUT_REDIRECT_URI=https://budget.stwaddle.com

src/Budget.Client/src/auth/authConfig.ts

@@ -1,11 +1,11 @@
 import type { UserManagerSettings } from 'oidc-client-ts';
 
 export const authConfig: UserManagerSettings = {
-  authority: import.meta.env.VITE_AUTH_AUTHORITY,
-  client_id: import.meta.env.VITE_AUTH_CLIENT_ID,
-  redirect_uri: import.meta.env.VITE_AUTH_REDIRECT_URI,
+  authority: import.meta.env.VITE_OIDC_AUTHORITY,
+  client_id: import.meta.env.VITE_OIDC_CLIENT_ID,
+  redirect_uri: import.meta.env.VITE_OIDC_REDIRECT_URI,
   response_type: 'code',
   scope: 'openid profile email offline_access budget_api',
-  post_logout_redirect_uri: import.meta.env.VITE_AUTH_REDIRECT_URI?.replace('/callback', ''),
+  post_logout_redirect_uri: import.meta.env.VITE_OIDC_POST_LOGOUT_REDIRECT_URI,
   automaticSilentRenew: true,
 };