feat: Introduce a web frontend with new city API routes and refactor bot city query logic into a dedicated service.

frontend/app/api/cities/route.ts

@@ -1,4 +1,5 @@
 import { NextResponse } from "next/server";
+import { buildBackendRequestHeaders } from "@/lib/backend-auth";
 
 const API_BASE = process.env.POLYWEATHER_API_BASE_URL;
 
@@ -12,7 +13,7 @@ export async function GET() {
 
   try {
     const res = await fetch(`${API_BASE}/api/cities`, {
-      headers: { Accept: "application/json" },
+      headers: buildBackendRequestHeaders(),
       next: { revalidate: 120 },
     });
     if (!res.ok) {

frontend/app/api/city/[name]/detail/route.ts

@@ -1,4 +1,5 @@
 import { NextRequest, NextResponse } from "next/server";
+import { buildBackendRequestHeaders } from "@/lib/backend-auth";
 
 const API_BASE = process.env.POLYWEATHER_API_BASE_URL;
 
@@ -26,7 +27,7 @@ export async function GET(
 
   try {
     const res = await fetch(url, {
-      headers: { Accept: "application/json" },
+      headers: buildBackendRequestHeaders(),
       cache: "no-store",
     });
     if (!res.ok) {

frontend/app/api/city/[name]/route.ts

@@ -1,4 +1,5 @@
 import { NextRequest, NextResponse } from "next/server";
+import { buildBackendRequestHeaders } from "@/lib/backend-auth";
 
 const API_BASE = process.env.POLYWEATHER_API_BASE_URL;
 
@@ -19,7 +20,7 @@ export async function GET(
 
   try {
     const res = await fetch(url, {
-      headers: { Accept: "application/json" },
+      headers: buildBackendRequestHeaders(),
       cache: "no-store",
     });
     if (!res.ok) {

frontend/app/api/city/[name]/summary/route.ts

@@ -1,4 +1,5 @@
 import { NextRequest, NextResponse } from "next/server";
+import { buildBackendRequestHeaders } from "@/lib/backend-auth";
 
 const API_BASE = process.env.POLYWEATHER_API_BASE_URL;
 
@@ -19,7 +20,7 @@ export async function GET(
 
   try {
     const res = await fetch(url, {
-      headers: { Accept: "application/json" },
+      headers: buildBackendRequestHeaders(),
       cache: "no-store",
     });
     if (!res.ok) {

frontend/app/api/history/[name]/route.ts

@@ -1,4 +1,5 @@
 import { NextResponse } from "next/server";
+import { buildBackendRequestHeaders } from "@/lib/backend-auth";
 
 const API_BASE = process.env.POLYWEATHER_API_BASE_URL;
 
@@ -18,7 +19,7 @@ export async function GET(
 
   try {
     const res = await fetch(url, {
-      headers: { Accept: "application/json" },
+      headers: buildBackendRequestHeaders(),
       cache: "no-store",
     });
     if (!res.ok) {

frontend/app/entitlement-required/page.tsx

@@ -0,0 +1,46 @@
+type Props = {
+  searchParams?: Promise<{ next?: string }>;
+};
+
+export default async function EntitlementRequiredPage({ searchParams }: Props) {
+  const params = (await searchParams) || {};
+  const nextPath = params.next || "/";
+
+  return (
+    <main
+      style={{
+        minHeight: "100vh",
+        display: "grid",
+        placeItems: "center",
+        background:
+          "radial-gradient(circle at 20% 20%, #13264f 0%, #071127 45%, #040812 100%)",
+        color: "#d6e2ff",
+        padding: "24px",
+      }}
+    >
+      <section
+        style={{
+          width: "100%",
+          maxWidth: 720,
+          border: "1px solid rgba(68, 92, 140, 0.45)",
+          borderRadius: 16,
+          padding: 24,
+          background: "rgba(9, 18, 36, 0.88)",
+          boxShadow: "0 20px 50px rgba(0, 0, 0, 0.35)",
+        }}
+      >
+        <h1 style={{ margin: 0, fontSize: 28, lineHeight: 1.2 }}>
+          Entitlement Required
+        </h1>
+        <p style={{ marginTop: 12, color: "#9fb2da", lineHeight: 1.6 }}>
+          This dashboard is protected. Append{" "}
+          <code>?access_token=&lt;your-token&gt;</code> to the URL once, and
+          the session cookie will be set automatically.
+        </p>
+        <p style={{ marginTop: 12, color: "#9fb2da", lineHeight: 1.6 }}>
+          Requested path: <code>{nextPath}</code>
+        </p>
+      </section>
+    </main>
+  );
+}