fix(widget): skip declaration bundling under Storybook build

Storybook's Vite builder loads vite.config.ts, so vite-plugin-dts ran during 'storybook build' and failed: api-extractor looked for dist/index.d.ts, which only the library build produces. Guard the dts plugin behind process.env.STORYBOOK so it runs only for the library build. Verified locally: 'pnpm build' still emits dist/index.d.ts (+ .d.cts) and 'pnpm build-storybook' now succeeds.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Paul Mulligan

widget/vite.config.ts

@@ -6,23 +6,31 @@ import { resolve } from "path";
 export default defineConfig({
   plugins: [
     react(),
-    dts({
-      // unplugin-dts (vite-plugin-dts v5) calls declaration bundling
-      // `bundleTypes` (the old `rollupTypes` name is ignored). This rolls the
-      // whole public surface into a single dist/index.d.ts via api-extractor.
-      bundleTypes: true,
-      tsconfigPath: "./tsconfig.json",
-      include: ["src"],
-      exclude: [
-        "src/**/*.test.ts",
-        "src/**/*.test.tsx",
-        "src/**/*.stories.tsx",
-        "src/test-setup.ts",
-        "src/test-utils/**",
-        "src/main.tsx",
-        "src/embed.tsx",
-      ],
-    }),
+    // Storybook's Vite builder also loads this config, but it builds to its own
+    // output (not dist/), so the declaration bundler would fail looking for
+    // dist/index.d.ts. Emit declarations only for the library build.
+    ...(process.env.STORYBOOK
+      ? []
+      : [
+          dts({
+            // unplugin-dts (vite-plugin-dts v5) calls declaration bundling
+            // `bundleTypes` (the old `rollupTypes` name is ignored). This rolls
+            // the whole public surface into a single dist/index.d.ts via
+            // api-extractor.
+            bundleTypes: true,
+            tsconfigPath: "./tsconfig.json",
+            include: ["src"],
+            exclude: [
+              "src/**/*.test.ts",
+              "src/**/*.test.tsx",
+              "src/**/*.stories.tsx",
+              "src/test-setup.ts",
+              "src/test-utils/**",
+              "src/main.tsx",
+              "src/embed.tsx",
+            ],
+          }),
+        ]),
   ],
   server: {
     port: 5173,