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/ui_compress.go

@@ -0,0 +1,81 @@
+package proxy
+
+import (
+	"net/http"
+	"strings"
+)
+
+// selectEncoding chooses the best encoding based on Accept-Encoding header
+// Returns the encoding ("br", "gzip", or "") and the corresponding file extension
+func selectEncoding(acceptEncoding string) (encoding, ext string) {
+	if acceptEncoding == "" {
+		return "", ""
+	}
+
+	for _, part := range strings.Split(acceptEncoding, ",") {
+		enc := strings.TrimSpace(strings.SplitN(part, ";", 2)[0])
+		if enc == "br" {
+			return "br", ".br"
+		}
+	}
+
+	for _, part := range strings.Split(acceptEncoding, ",") {
+		enc := strings.TrimSpace(strings.SplitN(part, ";", 2)[0])
+		if enc == "gzip" {
+			return "gzip", ".gz"
+		}
+	}
+
+	return "", ""
+}
+
+// ServeCompressedFile serves a file with compression support.
+// It checks for pre-compressed versions and serves them with proper headers.
+func ServeCompressedFile(fs http.FileSystem, w http.ResponseWriter, r *http.Request, name string) {
+	encoding, ext := selectEncoding(r.Header.Get("Accept-Encoding"))
+
+	// Try to serve compressed version if client supports it
+	if encoding != "" {
+		if cf, err := fs.Open(name + ext); err == nil {
+			defer cf.Close()
+
+			// Verify it's a regular file (not a directory)
+			if stat, err := cf.Stat(); err == nil && !stat.IsDir() {
+				// Set the content encoding header
+				w.Header().Set("Content-Encoding", encoding)
+				w.Header().Add("Vary", "Accept-Encoding")
+
+				// Get original file info for content type detection
+				origFile, err := fs.Open(name)
+				if err == nil {
+					origFile.Close()
+				}
+
+				// Serve the compressed file
+				http.ServeContent(w, r, name, stat.ModTime(), cf)
+				return
+			}
+		}
+	}
+
+	// Fall back to serving the uncompressed file
+	file, err := fs.Open(name)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusNotFound)
+		return
+	}
+	defer file.Close()
+
+	stat, err := file.Stat()
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+
+	if stat.IsDir() {
+		http.Error(w, "is a directory", http.StatusForbidden)
+		return
+	}
+
+	http.ServeContent(w, r, name, stat.ModTime(), file)
+}