Rebuild the admin dashboard as a Svelte 5 + TypeScript app

Frontend in web/ (Vite via bun, pure CSS, no component libraries),
built to internal/dashboard/dist and embedded into the binary; the
Dockerfile builds it in a bun stage. Old static dashboard.html removed.

web/vite.config.ts

@@ -0,0 +1,11 @@
+import { defineConfig } from "vite";
+import { svelte } from "@sveltejs/vite-plugin-svelte";
+
+// The build lands inside the Go package that embeds it.
+export default defineConfig({
+  plugins: [svelte()],
+  build: {
+    outDir: "../internal/dashboard/dist",
+    emptyOutDir: true,
+  },
+});