优化 Vercel Fluid CPU：API加CDN缓存、缩小middleware范围、跳过公共API的Supabase身份转发

- 7条GET路由加 s-maxage + stale-while-revalidate，fetch 改为 next revalidate
- middleware matcher 从全匹配缩小到9条需auth的路径，移除 isStaticAsset
- 8条公共API路由加 includeSupabaseIdentity: false
- backend-auth getSession 为空时跳过 getUser
- subscription-help 加 I18nProvider，移除 force-dynamic → 静态预渲染
- next.config.mjs 加静态资源 immutable 缓存头

Tested: npx tsc --noEmit 通过，npm run build 通过

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

@@ -7,6 +7,7 @@ import {
   buildProxyExceptionResponse,
   buildUpstreamErrorResponse,
 } from "@/lib/api-proxy";
+import { buildCachedJsonResponse } from "@/lib/http-cache";
 
 const API_BASE = process.env.POLYWEATHER_API_BASE_URL;
 
@@ -42,10 +43,12 @@ export async function GET(
   const url = `${API_BASE}/api/city/${encodeURIComponent(name)}/detail?${searchParams.toString()}`;
 
   try {
-    const auth = await buildBackendRequestHeaders(req);
+    const auth = await buildBackendRequestHeaders(req, {
+      includeSupabaseIdentity: false,
+    });
     const res = await fetch(url, {
       headers: auth.headers,
-      cache: "no-store",
+      next: { revalidate: 15 },
     });
     if (!res.ok) {
       const raw = await res.text();
@@ -53,7 +56,11 @@ export async function GET(
       return applyAuthResponseCookies(response, auth.response);
     }
     const data = await res.json();
-    const response = NextResponse.json(data);
+    const response = buildCachedJsonResponse(
+      req,
+      data,
+      "public, max-age=0, s-maxage=15, stale-while-revalidate=45",
+    );
     return applyAuthResponseCookies(response, auth.response);
   } catch (error) {
     const response = buildProxyExceptionResponse(error, {

frontend/app/api/city/[name]/market-scan/route.ts

@@ -7,6 +7,7 @@ import {
   buildProxyExceptionResponse,
   buildUpstreamErrorResponse,
 } from "@/lib/api-proxy";
+import { buildCachedJsonResponse } from "@/lib/http-cache";
 
 const API_BASE = process.env.POLYWEATHER_API_BASE_URL;
 
@@ -45,10 +46,12 @@ export async function GET(
   const url = `${API_BASE}/api/city/${encodeURIComponent(name)}/market-scan?${params.toString()}`;
 
   try {
-    const auth = await buildBackendRequestHeaders(req);
+    const auth = await buildBackendRequestHeaders(req, {
+      includeSupabaseIdentity: false,
+    });
     const res = await fetch(url, {
       headers: auth.headers,
-      cache: "no-store",
+      next: { revalidate: 20 },
     });
     if (!res.ok) {
       const raw = await res.text();
@@ -59,11 +62,11 @@ export async function GET(
       return applyAuthResponseCookies(response, auth.response);
     }
     const data = await res.json();
-    const response = NextResponse.json(data, {
-      headers: {
-        "Cache-Control": "no-store",
-      },
-    });
+    const response = buildCachedJsonResponse(
+      req,
+      data,
+      "public, max-age=0, s-maxage=20, stale-while-revalidate=60",
+    );
     return applyAuthResponseCookies(response, auth.response);
   } catch (error) {
     const response = buildProxyExceptionResponse(error, {

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

@@ -7,6 +7,7 @@ import {
   buildProxyExceptionResponse,
   buildUpstreamErrorResponse,
 } from "@/lib/api-proxy";
+import { buildCachedJsonResponse } from "@/lib/http-cache";
 
 const API_BASE = process.env.POLYWEATHER_API_BASE_URL;
 
@@ -131,26 +132,28 @@ export async function GET(
   const url = `${API_BASE}/api/city/${encodeURIComponent(name)}?force_refresh=${forceRefresh}&depth=${encodeURIComponent(depth)}`;
 
   try {
-    const auth = await buildBackendRequestHeaders(req);
+    const auth = await buildBackendRequestHeaders(req, {
+      includeSupabaseIdentity: false,
+    });
     const res = await fetch(url, {
       headers: auth.headers,
-      cache: "no-store",
+      next: { revalidate: 15 },
     });
     if (!res.ok) {
       const raw = await res.text();
       const summaryUrl = `${API_BASE}/api/city/${encodeURIComponent(name)}/summary?force_refresh=${forceRefresh}`;
       const summaryRes = await fetch(summaryUrl, {
         headers: auth.headers,
-        cache: "no-store",
+        next: { revalidate: 10 },
       });
       if (summaryRes.ok) {
         const summaryData = await summaryRes.json();
-        const response = NextResponse.json(buildFallbackCityDetail(name, depth, summaryData), {
-          headers: {
-            "Cache-Control": "no-store",
-            "X-PolyWeather-Fallback": "summary",
-          },
-        });
+        const response = buildCachedJsonResponse(
+          req,
+          buildFallbackCityDetail(name, depth, summaryData),
+          "public, max-age=0, s-maxage=10, stale-while-revalidate=30",
+        );
+        response.headers.set("X-PolyWeather-Fallback", "summary");
         return applyAuthResponseCookies(response, auth.response);
       }
 
@@ -158,7 +161,11 @@ export async function GET(
       return applyAuthResponseCookies(response, auth.response);
     }
     const data = normalizeCityDetailPayload(await res.json());
-    const response = NextResponse.json(data);
+    const response = buildCachedJsonResponse(
+      req,
+      data,
+      "public, max-age=0, s-maxage=15, stale-while-revalidate=45",
+    );
     return applyAuthResponseCookies(response, auth.response);
   } catch (error) {
     const response = buildProxyExceptionResponse(error, {