Migrate from Next.js to SvelteKit

- Replace Next.js app with SvelteKit + adapter-node
- basePath /bodenfeuchte configured in svelte.config.js
- MQTT listener starts via hooks.server.ts on server boot
- Chart.js replaces Recharts for the moisture graph
- Dockerfile simplified: single build step, node build output
- Removed custom server.ts (no longer needed)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

vite.config.ts

@@ -0,0 +1,6 @@
+import { sveltekit } from '@sveltejs/kit/vite';
+import { defineConfig } from 'vite';
+
+export default defineConfig({
+	plugins: [sveltekit()]
+});