feat: persistance des filtres server-side via cookies

Remplace localStorage par des cookies pour la persistance des filtres.
Le proxy restaure les filtres sauvegardés côté serveur, éliminant le flash au chargement.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/backoffice/proxy.ts

@@ -8,8 +8,16 @@ function getSecret(): Uint8Array {
   return new TextEncoder().encode(secret);
 }
 
+/** Paths where filter persistence is active */
+const FILTER_PATHS = ["/series", "/books", "/authors"];
+
+/** Convert a basePath to a cookie name: /series → filters_series */
+function filterCookieName(basePath: string): string {
+  return `filters_${basePath.replace(/^\//, "").replace(/\//g, "_")}`;
+}
+
 export async function proxy(req: NextRequest) {
-  const { pathname } = req.nextUrl;
+  const { pathname, searchParams } = req.nextUrl;
 
   // Skip auth for login page and auth API routes
   if (pathname.startsWith("/login") || pathname.startsWith("/api/auth")) {
@@ -20,10 +28,38 @@ export async function proxy(req: NextRequest) {
   if (token) {
     try {
       await jwtVerify(token, getSecret());
-      return NextResponse.next();
     } catch {
-      // Token invalid or expired
+      // Token invalid or expired — redirect to login
+      const loginUrl = new URL("/login", req.url);
+      loginUrl.searchParams.set("from", pathname);
+      return NextResponse.redirect(loginUrl);
     }
+
+    // Restore saved filters from cookie for filter pages
+    if (FILTER_PATHS.includes(pathname)) {
+      const nonPaginationParams = Array.from(searchParams.entries()).filter(
+        ([key]) => key !== "page" && key !== "limit"
+      );
+      if (nonPaginationParams.length === 0) {
+        const cookieName = filterCookieName(pathname);
+        const cookie = req.cookies.get(cookieName);
+        if (cookie?.value) {
+          try {
+            const filters: Record<string, string> = JSON.parse(cookie.value);
+            const entries = Object.entries(filters).filter(([, v]) => v && v.trim());
+            if (entries.length > 0) {
+              const url = req.nextUrl.clone();
+              for (const [key, value] of entries) {
+                url.searchParams.set(key, value);
+              }
+              return NextResponse.redirect(url);
+            }
+          } catch {}
+        }
+      }
+    }
+
+    return NextResponse.next();
   }
 
   const loginUrl = new URL("/login", req.url);