proxy,ui-svelte: replace old UI with svelte+playground

Replace the legacy React UI with the new Svelte-based one. Introduce a Playground in the UI to quickly test out text, image, text to speech and speech to text models behind llama-swap. 

Key Changes

New Svelte UI (ui-svelte/)

  - Multi-tab Playground with Chat, Image Generation, Audio Transcription, and Speech interfaces
  - Chat: message editing/regeneration, markdown rendering with LaTeX math support, image attachments, code syntax highlighting
  - Image: size selector, download/fullscreen viewing
  - Audio: transcription with peer support
  - Speech: voice caching with manual refresh, download button
  - Responsive mobile layout with collapsible navigation
  - XSS fixes and accessibility improvements

Proxy Improvements

  - Add gzip/brotli compression for UI static assets (proxy/ui_compress.go)
  - Add GET /v1/audio/voices?model={model} endpoint for voice listing
  - Add peer support for /v1/audio/transcriptions

proxy/helpers_test.go

@@ -71,11 +71,15 @@ func getTestSimpleResponderConfig(expectedMessage string) config.ModelConfig {
 }
 
 func getTestSimpleResponderConfigPort(expectedMessage string, port int) config.ModelConfig {
+	// Convert path to forward slashes for cross-platform compatibility
+	// Windows handles forward slashes in paths correctly
+	cmdPath := filepath.ToSlash(simpleResponderPath)
+
 	// Create a YAML string with just the values we want to set
 	yamlStr := fmt.Sprintf(`
 cmd: '%s --port %d --silent --respond %s'
 proxy: "http://127.0.0.1:%d"
-`, simpleResponderPath, port, expectedMessage, port)
+`, cmdPath, port, expectedMessage, port)
 
 	var cfg config.ModelConfig
 	if err := yaml.Unmarshal([]byte(yamlStr), &cfg); err != nil {