fix: replace NEXT_PUBLIC_API_URL with Next.js Route Handler proxy for runtime backend URL

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>
Agent-Logs-Url: https://github.com/christianlouis/pop_puller_to_gmail/sessions/59e2f604-9ad3-46ef-8670-fd6b3b7c14b2

frontend/src/app/api/v1/[...path]/route.ts

@@ -0,0 +1,43 @@
+import { NextRequest, NextResponse } from "next/server";
+
+const BACKEND_URL = process.env.BACKEND_URL ?? "http://localhost:8000";
+
+type RouteContext = { params: Promise<{ path: string[] }> };
+
+async function handler(request: NextRequest, context: RouteContext) {
+  const { path } = await context.params;
+  const targetUrl = `${BACKEND_URL}/api/v1/${path.join("/")}${request.nextUrl.search}`;
+
+  const headers = new Headers(request.headers);
+  headers.delete("host");
+  // Request uncompressed response so the body can be forwarded as-is
+  headers.set("accept-encoding", "identity");
+
+  const hasBody = request.method !== "GET" && request.method !== "HEAD";
+  const body = hasBody ? await request.arrayBuffer() : undefined;
+
+  try {
+    const upstream = await fetch(targetUrl, {
+      method: request.method,
+      headers,
+      body,
+    });
+
+    return new NextResponse(upstream.body, {
+      status: upstream.status,
+      statusText: upstream.statusText,
+      headers: upstream.headers,
+    });
+  } catch (error) {
+    console.error("Proxy error forwarding to backend:", error);
+    return NextResponse.json({ detail: "Backend unavailable" }, { status: 502 });
+  }
+}
+
+export const GET = handler;
+export const POST = handler;
+export const PUT = handler;
+export const PATCH = handler;
+export const DELETE = handler;
+export const HEAD = handler;
+export const OPTIONS = handler;

frontend/src/lib/api.ts

@@ -1,10 +1,7 @@
 import axios from "axios";
 
-const API_BASE_URL =
-  process.env.NEXT_PUBLIC_API_URL || "http://localhost:8000";
-
 const api = axios.create({
-  baseURL: `${API_BASE_URL}/api/v1`,
+  baseURL: `/api/v1`,
   headers: {
     "Content-Type": "application/json",
   },