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/.eslintrc.json

@@ -1,6 +0,0 @@
-{
-  "env": {
-    "browser": true,
-    "node": false
-  }
-}

ui/autocomplete-compnent.ts

@@ -119,7 +119,9 @@ export default class Autocomplete {
       if (!this.visible) {
         if (!this.hideTimeout) {
           document.body.appendChild(this.container);
-          window.getComputedStyle(this.container).opacity;
+          // Force style recalc so the initial opacity is resolved before
+          // setting it to "1", allowing the CSS transition to play.
+          void window.getComputedStyle(this.container).opacity;
         } else {
           clearTimeout(this.hideTimeout);
           this.hideTimeout = null;

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
       }
 

ui/config-page.ts

@@ -31,7 +31,7 @@ function putActionHandler(action, _object, isNew?): Promise<ValidationErrors> {
 
       try {
         object.value = stringify(parse(object.value || ""));
-      } catch (err) {
+      } catch {
         return void resolve({
           value: "Config value must be valid expression",
         });

ui/filter-component.ts

@@ -83,7 +83,7 @@ const component: ClosureComponent<Attrs> = (initialVnode) => {
     const list = filterList.map((f, idx) => {
       try {
         return parseFilter(attrs.resource, f);
-      } catch (err) {
+      } catch {
         filterInvalid |= 1 << idx;
       }
       return null;

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",
           });

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",
           });

ui/store.ts

@@ -113,7 +113,7 @@ function checkConnection(): void {
             setTimestamp(now2);
             m.redraw();
           }
-        } catch (err) {
+        } catch {
           // Ignore in case of missing or invalid Date header
         }
 
@@ -200,7 +200,9 @@ export async function xhrRequest(
       try {
         response = xhr.responseText ? JSON.parse(xhr.responseText) : null;
       } catch (err) {
-        throw new Error("Invalid JSON: " + xhr.responseText.slice(0, 80));
+        throw new Error("Invalid JSON: " + xhr.responseText.slice(0, 80), {
+          cause: err,
+        });
       }
     } else {
       response = xhr.responseText;