feat: modernize UI with Astro+Svelte and optimize Docker build

- Migrated frontend to Astro + Svelte 5 for cyberpunk aesthetic
- Switched to Bun for faster frontend builds
- Implemented multi-stage Docker build for smaller image size
- Refactored backend to serve static assets and proxy API requests
- Added recovery mode for manual file management

ui/astro.config.mjs

@@ -0,0 +1,14 @@
+// @ts-check
+import { defineConfig } from 'astro/config';
+
+import svelte from '@astrojs/svelte';
+import tailwindcss from '@tailwindcss/vite';
+
+// https://astro.build/config
+export default defineConfig({
+  integrations: [svelte()],
+
+  vite: {
+    plugins: [tailwindcss()]
+  }
+});