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

ui-svelte/vite.config.ts

@@ -1,10 +1,25 @@
 import { defineConfig } from "vite";
 import { svelte } from "@sveltejs/vite-plugin-svelte";
 import tailwindcss from "@tailwindcss/vite";
+import { compression } from "vite-plugin-compression2";
 
 // https://vite.dev/config/
 export default defineConfig({
-  plugins: [svelte(), tailwindcss()],
+  plugins: [
+    svelte(),
+    tailwindcss(),
+    compression({
+      algorithm: "gzip",
+      exclude: [/\.(br)$/, /\.(gz)$/],
+      threshold: 1024,
+    }),
+    compression({
+      algorithm: "brotliCompress",
+      exclude: [/\.(br)$/, /\.(gz)$/],
+      threshold: 1024,
+      filename: "[path][base].br",
+    }),
+  ],
   base: "/ui/",
   build: {
     outDir: "../proxy/ui_dist",
@@ -16,6 +31,7 @@ export default defineConfig({
       "/logs": "http://localhost:8080",
       "/upstream": "http://localhost:8080",
       "/unload": "http://localhost:8080",
+      "/v1": "http://localhost:8080",
     },
   },
 });