chore: enhance frontend configuration for backend integration

- Added environment variables for backend URLs in the Dockerfile to facilitate dynamic configuration.
- Updated Next.js configuration to include rewrites for health and API endpoints, improving backend connectivity.
- Modified settings page to handle backend URL locking and normalization, enhancing user experience and data integrity.

app/(main)/settings/page.tsx

@@ -825,7 +825,7 @@ export default function SettingsPage() {
   const [copied,   setCopied]   = useState<string | null>(null)
 
   // data source
-  const { mode, setMode, backendUrl, setBackendUrl, backendStatus, checkBackend } = useDataSource()
+  const { mode, setMode, backendUrl, setBackendUrl, backendUrlLocked, backendStatus, checkBackend } = useDataSource()
   const evo = useEvoBGP()
   const [evoBaseDraft, setEvoBaseDraft] = useState("")
   const [evoEnabledDraft, setEvoEnabledDraft] = useState(false)
@@ -834,6 +834,17 @@ export default function SettingsPage() {
   const [evoSaveErr, setEvoSaveErr] = useState<string | null>(null)
   const [urlDraft, setUrlDraft] = useState(backendUrl)
   const apiFetch = useMemo(() => makeApiFetch(backendUrl), [backendUrl])
+
+  useEffect(() => {
+    setUrlDraft(backendUrl)
+  }, [backendUrl])
+
+  const commitBackendUrl = useCallback(() => {
+    const normalized = urlDraft.trim().replace(/\/$/, "")
+    setUrlDraft(normalized)
+    setBackendUrl(normalized)
+    void checkBackend()
+  }, [urlDraft, setBackendUrl, checkBackend])
   const [evoTestResult, setEvoTestResult] = useState<{ ok: boolean; message: string } | null>(null)
   const [evoBusy, setEvoBusy] = useState<"test" | "refresh" | null>(null)
   const [showEvoKey, setShowEvoKey] = useState(false)
@@ -984,17 +995,31 @@ export default function SettingsPage() {
           </SettingRow>
 
           {/* backend URL — visible in both modes so user can configure before switching */}
-          <SettingRow label="URL бекенда" description="Адрес Node.js/Fastify сервера (запускается командой npm run dev в /backend)">
+          <SettingRow
+            label="URL бекенда"
+            description={
+              backendUrlLocked
+                ? "В Docker-образе URL API задаётся через прокси фронтенда на backend; поле только для просмотра."
+                : "Адрес Node.js/Fastify сервера (запускается командой npm run dev в /backend)"
+            }
+          >
             <div className="flex items-center gap-2">
               <Input
                 className="w-56 h-8 text-sm font-mono"
                 value={urlDraft}
                 onChange={e => setUrlDraft(e.target.value)}
-                onBlur={() => { setBackendUrl(urlDraft.replace(/\/$/, "")) }}
+                onBlur={commitBackendUrl}
+                onKeyDown={e => {
+                  if (e.key === "Enter") {
+                    e.preventDefault()
+                    commitBackendUrl()
+                  }
+                }}
+                readOnly={backendUrlLocked}
                 placeholder="http://localhost:8000"
               />
               <Button variant="outline" size="sm" className="h-8 px-2.5 shrink-0"
-                onClick={() => { setBackendUrl(urlDraft.replace(/\/$/, "")); checkBackend() }}
+                onClick={commitBackendUrl}
                 title="Проверить соединение">
                 <RefreshCwIcon className="size-3.5" />
               </Button>