build(ui): upgrade TypeScript 7 and align Node 26 toolchain (#3379)

Read the CI Node version from UI engines and match Docker and Node types.\nDocument the native compiler workflow without changing UI dependencies.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: SamMorrowDrums

.github/actions/build-ui/action.yml

@@ -20,7 +20,7 @@ runs:
       if: steps.cache-ui.outputs.cache-hit != 'true'
       uses: actions/setup-node@v7
       with:
-        node-version: "22"
+        node-version-file: ui/package.json
         cache: npm
         cache-dependency-path: ui/package-lock.json
 

.github/workflows/code-scanning.yml

@@ -82,7 +82,7 @@ jobs:
         if: matrix.language == 'javascript'
         uses: actions/setup-node@v7
         with:
-          node-version: "20"
+          node-version-file: ui/package.json
           cache: "npm"
           cache-dependency-path: ui/package-lock.json
 

CONTRIBUTING.md

@@ -29,6 +29,17 @@ These are one time installations required to be able to test your changes locall
 1. Install Go 1.26.8 or later [through download](https://go.dev/doc/install) | [through Homebrew](https://formulae.brew.sh/formula/go)
 2. [Install golangci-lint v2.14.0](https://golangci-lint.run/welcome/install/#local-installation), or let `script/lint` install the repository-pinned version. The pinned version supports both Go 1.26 and Go 1.27.
 
+### UI development
+
+Use Node.js 26.x for the UI in `ui/`. This matches the Docker UI build stage
+and `@types/node`; GitHub Actions reads the Node version from `ui/package.json`.
+Node 26 is a supported Current release, with LTS scheduled for October 2026.
+
+From `ui/`, run `npm ci`, `npm run typecheck`, and `npm run build`.
+Type checking uses the native TypeScript 7 compiler through `tsc`; Vite handles
+transpilation and bundling separately. No TypeScript compiler API integration,
+typescript-eslint, or ts-node is required.
+
 ## Submitting a pull request
 
 1. [Fork][fork] and clone the repository