fix(site-finder): address PR #86 auto-review minor recommendations

- Use usePathname() for router.replace fallback (avoid dangling "?" in Next 15)
- Remove stale-closure guard in useEffect — React bails Object.is, no eslint-disable
- Wrap page in <Suspense> for useSearchParams (Next 15 App Router req for static)
- Lazy useState initializer — skip wasted CPU on re-renders

Per auto-review on c47e56b.

frontend/src/app/site-finder/page.tsx

@@ -1,9 +1,9 @@
 "use client";
 
-import { useEffect, useState } from "react";
+import { Suspense, useEffect, useState } from "react";
 import dynamic from "next/dynamic";
 import Link from "next/link";
-import { useRouter, useSearchParams } from "next/navigation";
+import { usePathname, useRouter, useSearchParams } from "next/navigation";
 import type { FeatureCollection } from "geojson";
 
 import { CadInput } from "@/components/site-finder/CadInput";
@@ -80,19 +80,21 @@ function scoreKpiColor(score: number, max: number): KpiColor {
 
 // ── Page ──────────────────────────────────────────────────────────────────────
 
-export default function SiteFinderPage() {
+function SiteFinderContent() {
   const router = useRouter();
+  const pathname = usePathname();
   const searchParams = useSearchParams();
-  const initialTab: TabId = (() => {
-    const t = searchParams.get("tab");
-    return isTabId(t) ? t : "overview";
-  })();
 
   const { mutate, data, isPending, error, isIdle } = useSiteAnalysis();
   const [isochrones, setIsochrones] = useState<FeatureCollection | undefined>(
     undefined,
   );
-  const [tab, setTabState] = useState<TabId>(initialTab);
+  // Lazy init: считаем initialTab один раз на mount (useState всё равно
+  // игнорирует initializer после первого render — не тратим CPU).
+  const [tab, setTabState] = useState<TabId>(() => {
+    const t = searchParams.get("tab");
+    return isTabId(t) ? t : "overview";
+  });
 
   // Sync tab → URL query (?tab=env). overview = default, не пишем в URL.
   function setTab(next: TabId) {
@@ -104,15 +106,17 @@ export default function SiteFinderPage() {
       params.set("tab", next);
     }
     const qs = params.toString();
-    router.replace(qs ? `?${qs}` : "?", { scroll: false });
+    // Используем pathname вместо голого "?" — Next 15 App Router не всегда
+    // чисто чистит query при `router.replace("?")` (dangling `?` остаётся).
+    router.replace(qs ? `${pathname}?${qs}` : pathname, { scroll: false });
   }
 
-  // Listen to back/forward navigation — reflect URL tab in state
+  // Listen to back/forward navigation — reflect URL tab in state.
+  // setState с тем же значением React сам бэйлит через Object.is, поэтому
+  // guard по tab не нужен (и не вводит stale-closure через eslint-disable).
   useEffect(() => {
     const urlTab = searchParams.get("tab");
-    const validTab: TabId = isTabId(urlTab) ? urlTab : "overview";
+    setTabState(isTabId(urlTab) ? urlTab : "overview");
-    if (validTab !== tab) setTabState(validTab);
-    // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [searchParams]);
 
   function handleAnalyze(cadNum: string) {
@@ -377,3 +381,13 @@ export default function SiteFinderPage() {
     </main>
   );
 }
+
+// useSearchParams() в Next 15 App Router throw'ит при static rendering без
+// <Suspense> boundary — поэтому оборачиваем page-level.
+export default function SiteFinderPage() {
+  return (
+    <Suspense fallback={null}>
+      <SiteFinderContent />
+    </Suspense>
+  );
+}