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/src/lib/modelUtils.ts

@@ -0,0 +1,24 @@
+import type { Model } from "./types";
+
+export interface GroupedModels {
+  local: Model[];
+  peersByProvider: Record<string, Model[]>;
+}
+
+export function groupModels(models: Model[]): GroupedModels {
+  const available = models.filter((m) => !m.unlisted);
+  const local = available.filter((m) => !m.peerID);
+  const peerModels = available.filter((m) => m.peerID);
+
+  const peersByProvider = peerModels.reduce(
+    (acc, model) => {
+      const peerId = model.peerID || "unknown";
+      if (!acc[peerId]) acc[peerId] = [];
+      acc[peerId].push(model);
+      return acc;
+    },
+    {} as Record<string, Model[]>
+  );
+
+  return { local, peersByProvider };
+}