refactor(env): centralize auth env handling and prefer BETTER_AUTH_BASE_URL

Backend/auth.ts

@@ -3,6 +3,7 @@ import { drizzleAdapter } from 'better-auth/adapters/drizzle';
 
 import { db } from './db/client';
 import { schema } from './db/schema';
+import { getBetterAuthBaseUrl, getRequiredEnv } from './utils/env';
 import { hashPassword, verifyPassword } from './utils/password';
 
 const trustedOrigins = process.env.BETTER_AUTH_TRUSTED_ORIGINS
@@ -24,8 +25,8 @@ export const auth = betterAuth({
       verify: async ({ hash, password }) => verifyPassword(password, hash),
     },
   },
-  secret: process.env.BETTER_AUTH_SECRET,
-  baseURL: process.env.BETTER_AUTH_URL,
+  secret: getRequiredEnv('BETTER_AUTH_SECRET'),
+  baseURL: getBetterAuthBaseUrl(),
   trustedOrigins,
 });