chore(lint): upgrade no-unused-vars rule from warn to error

Flip @typescript-eslint/no-unused-vars from "warn" to "error" in
oxlint.json (with argsIgnorePattern/varsIgnorePattern of "^_" and
caughtErrors "none"), and clean up the resulting violations across the
frontend.

Fixes favor proper cleanup over underscore hacks: genuinely dead
imports, variables, and destructured props are removed; parameters are
only "_"-prefixed when their position is required by an external or
callback signature (event handlers, render props, antd validators,
forwardRef, or omit-from-rest destructuring).

Note: the .eslintrc.js half of the prior attempt (#37886) is obsolete
since the frontend migrated to oxlint as the primary linter.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

superset-frontend/src/components/ErrorMessage/FrontendNetworkErrorMessage.tsx

@@ -23,7 +23,6 @@ import { ErrorAlert } from './ErrorAlert';
 
 export function FrontendNetworkErrorMessage({
   error,
-  subtitle,
   compact,
   closable,
 }: ErrorMessageComponentProps) {