build: migrate eslint to v10 flat config and upgrade typescript

Replace .eslintrc.json with eslint.config.js using the new flat config
format required by ESLint 10. Swap @typescript-eslint/eslint-plugin and
@typescript-eslint/parser for the unified typescript-eslint package.
Upgrade TypeScript to 5.9 and @types/node to 25. Apply automatic code
fixes: remove unused catch bindings and preserve error cause in auth
header parsing.

ui/components/ping.ts

@@ -47,7 +47,7 @@ const component: ClosureComponent = (vn): Component => {
       try {
         const url = new URL(param.value[0]);
         h = url.hostname;
-      } catch (err) {
+      } catch {
         // Ignore
       }