fix(docs-next): resolve @stackoverflow/stacks via ESM entry for Rollup

Rollup (used by Vite for production builds) cannot statically extract
named exports from webpack's UMD bundle format, causing
"hidePopover is not exported" when stacks-editor's ESM source imports
from @stackoverflow/stacks.

- Add lib/esm-no-css.ts: an ESM entry that mirrors lib/index.ts but
  omits the CSS side-effect (the docs site imports the CSS directly
  via app.css)
- Alias @stackoverflow/stacks to this entry in vite.config.ts (exact
  match via regex; subpath imports like /dist/css/stacks.css are
  unaffected)

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

Author: dancormier

packages/stacks-classic/lib/esm-no-css.ts

@@ -0,0 +1,26 @@
+// ESM entry for bundlers that need named exports (e.g. Vite/Rollup).
+// Mirrors lib/index.ts but omits the CSS side-effect import;
+// consumers should import the stylesheet separately.
+import {
+    BannerController,
+    ModalController,
+    PopoverController,
+    TableController,
+    TabListController,
+    ToastController,
+    TooltipController,
+} from "./controllers";
+import { application, StacksApplication } from "./stacks";
+
+application.register("s-banner", BannerController);
+application.register("s-modal", ModalController);
+application.register("s-toast", ToastController);
+application.register("s-navigation-tablist", TabListController);
+application.register("s-popover", PopoverController);
+application.register("s-table", TableController);
+application.register("s-tooltip", TooltipController);
+
+StacksApplication.finalize();
+
+export * from "./controllers";
+export * from "./stacks";

packages/stacks-docs-next/vite.config.ts

@@ -1,10 +1,14 @@
 import fs from "fs";
+import { fileURLToPath } from "url";
+import { dirname, resolve } from "path";
 import { sveltekit } from "@sveltejs/kit/vite";
 import { defineConfig } from "vite";
 
 import pkgMain from "../stacks-classic/package.json";
 import pkgSvelte from "../stacks-svelte/package.json";
 
+const __dirname = dirname(fileURLToPath(import.meta.url));
+
 export default defineConfig({
     plugins: [
         sveltekit(),
@@ -18,6 +22,15 @@ export default defineConfig({
             },
         },
     ],
+    resolve: {
+        alias: [
+            {
+                // Exact match only — subpath imports like /dist/css/stacks.css are unaffected
+                find: /^@stackoverflow\/stacks$/,
+                replacement: resolve(__dirname, "../stacks-classic/lib/esm-no-css.ts"),
+            },
+        ],
+    },
     define: {
         __APP_VERSION__: JSON.stringify(pkgMain.version),
         __SVELTE_VERSION__: JSON.stringify(pkgSvelte.version),