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/go-ci-windows.yml

@@ -3,9 +3,25 @@ name: Windows CI
 on:
   push:
     branches: [ "main" ]
+    # only run when backend source changes
+    # cmd/ is excluded because it contains utilities without tests
+    paths:
+      - '**/*.go'
+      - '!cmd/**'
+      - 'go.mod'
+      - 'go.sum'
+      - 'Makefile'
+      - '.github/workflows/go-ci-windows.yml'
 
   pull_request:
     branches: [ "main" ]
+    paths:
+      - '**/*.go'
+      - '!cmd/**'
+      - 'go.mod'
+      - 'go.sum'
+      - 'Makefile'
+      - '.github/workflows/go-ci-windows.yml'
 
   # Allows manual triggering of the workflow
   workflow_dispatch: