Add path filters to CI workflows and create UI test workflow (#501)

* .github/workflows: add UI tests and path-filter Go CI

Add ui-tests.yml workflow to run svelte type checking and vitest
on push/PR to main when ui-svelte/ files change.

- Add path filters to go-ci.yml and go-ci-windows.yml to skip
  Go tests when only non-backend files change
- Filter on **/*.go, go.mod, go.sum, and Makefile

https://claude.ai/code/session_01E6acq54D8JjuE7pczxPGT7

* ui-svelte: remove unused declarations in SpeechInterface

Remove unused `generatedText` state and `clearAudio` function
that caused svelte-check errors.

https://claude.ai/code/session_01E6acq54D8JjuE7pczxPGT7

* .github/workflows: update Node.js to v24

Node 23 is end-of-life; bump to 24 in ui-tests.yml and release.yml.

https://claude.ai/code/session_01E6acq54D8JjuE7pczxPGT7

---------

Co-authored-by: Claude <noreply@anthropic.com>

.github/workflows/release.yml

@@ -29,7 +29,7 @@ jobs:
       - name: Set up Node.js
         uses: actions/setup-node@v4
         with:
-          node-version: "23"
+          node-version: "24"
       - name: Install dependencies and build UI
         run: |
           cd ui-svelte