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>

ui-svelte/src/components/playground/SpeechInterface.svelte

@@ -12,7 +12,6 @@
   let inputText = $state("");
   let isGenerating = $state(false);
   let generatedAudioUrl = $state<string | null>(null);
-  let generatedText = $state<string | null>(null);
   let generatedVoice = $state<string | null>(null);
   let generatedTimestamp = $state<Date | null>(null);
   let error = $state<string | null>(null);
@@ -148,7 +147,6 @@
 
       // Create object URL for the audio blob and store metadata
       generatedAudioUrl = URL.createObjectURL(audioBlob);
-      generatedText = trimmedText;
       generatedVoice = $selectedVoiceStore;
       generatedTimestamp = new Date();
     } catch (err) {
@@ -167,18 +165,6 @@
     abortController?.abort();
   }
 
-  function clearAudio() {
-    if (generatedAudioUrl) {
-      URL.revokeObjectURL(generatedAudioUrl);
-    }
-    generatedAudioUrl = null;
-    generatedText = null;
-    generatedVoice = null;
-    generatedTimestamp = null;
-    error = null;
-    inputText = "";
-  }
-
   function clearInput() {
     inputText = "";
   }