refactor: simplify request handlers and deduplicate config

- Re-enable TanStack Query retry (retry: 3 with exponential backoff),
  delete all server-side retry logic from request handlers
- Strip handler factories to bare minimum: remove isValid, retry, widgetKind
- Remove redundant refetchOnWindowFocus/refetchOnReconnect from docker-table
- Deduplicate queryCacheMaxValueBytes (pass as param, single source of truth)
- Simplify system-resources chart: use dataUpdatedAt instead of ref-based tracking
- Fix leading blank lines in 27 request handler files

packages/request-handler/src/docker.ts

@@ -172,7 +172,6 @@ const mockContainers: {
 
 export const dockerContainersRequestHandler = createWidgetRequestHandler({
   queryKey: "dockerContainersResult",
-  widgetKind: "dockerContainers",
   async requestAsync() {
     if (isDemoMode) {
       return mockContainers;