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/presets-page.ts

@@ -72,7 +72,7 @@ function putActionHandler(action, _object, isNew): Promise<ValidationErrors> {
       if (object.precondition) {
         try {
           object.precondition = stringify(memoizedParse(object.precondition));
-        } catch (err) {
+        } catch {
           return void resolve({
             precondition: "Precondition must be valid expression",
           });