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/permissions-page.ts

@@ -90,7 +90,7 @@ function putActionHandler(action, _object, isNew): Promise<ValidationErrors> {
       if (object.filter) {
         try {
           object.filter = stringify(memoizedParse(object.filter));
-        } catch (err) {
+        } catch {
           return void resolve({
             filter: "Filter must be valid expression",
           });
@@ -100,7 +100,7 @@ function putActionHandler(action, _object, isNew): Promise<ValidationErrors> {
       if (object.validate) {
         try {
           object.validate = stringify(memoizedParse(object.validate));
-        } catch (err) {
+        } catch {
           return void resolve({
             validate: "Validate must be valid expression",
           });