Add basic-server-vanillajs example

Demonstrates MCP App SDK usage with vanilla JavaScript (no framework),
providing parity with the existing basic-server-react example.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

examples/basic-server-vanillajs/vite.config.ts

@@ -0,0 +1,24 @@
+import { defineConfig } from "vite";
+import { viteSingleFile } from "vite-plugin-singlefile";
+
+const INPUT = process.env.INPUT;
+if (!INPUT) {
+  throw new Error("INPUT environment variable is not set");
+}
+
+const isDevelopment = process.env.NODE_ENV === "development";
+
+export default defineConfig({
+  plugins: [viteSingleFile()],
+  build: {
+    sourcemap: isDevelopment ? "inline" : undefined,
+    cssMinify: !isDevelopment,
+    minify: !isDevelopment,
+
+    rollupOptions: {
+      input: INPUT,
+    },
+    outDir: "dist",
+    emptyOutDir: false,
+  },
+});