Update build and lint workflows to Node.js 20.x (#654)

* Initial plan

* Update build and lint workflows to use Node.js 20.x

Co-authored-by: jbouder <[email protected]>

---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: jbouder <[email protected]>

Author: Copilot

.github/workflows/build-ui.yml

@@ -34,7 +34,7 @@ jobs:
       - name: Set up Node environment
         uses: actions/[email protected]
         with:
-          node-version: 18.x
+          node-version: 20.x
 
       - name: Install dependencies
         run: npm ci

.github/workflows/lint-ui.yml

@@ -17,7 +17,7 @@ jobs:
       - name: Set up Node environment
         uses: actions/[email protected]
         with:
-          node-version: 18.x
+          node-version: 20.x
 
       - name: Install dependencies
         run: npm ci