Backend: add PUBLIC_BASE_PATH for NIP-98 URL behind /api proxy

Made-with: Cursor

backend/src/config.ts

@@ -24,6 +24,8 @@ function envBool(key: string, defaultValue: boolean): boolean {
 export const config = {
   port: envInt("PORT", 3001),
   trustProxy: envBool("TRUST_PROXY", false),
+  /** Public path prefix when behind a reverse proxy that strips it (e.g. nginx /api/ -> backend /). */
+  publicBasePath: (process.env.PUBLIC_BASE_PATH ?? "").replace(/\/$/, ""),
   allowedOrigins: (process.env.ALLOWED_ORIGINS ?? process.env.FRONTEND_URL ?? "http://localhost:5173,http://localhost:5174").split(",").map((s) => s.trim()),
 
   // Database: omit DATABASE_URL for SQLite; set for Postgres