add tsconfig for storybook files and fix ImagePreview story

Add tsconfig.storybook.json to cover *.stories.tsx files excluded by
tsconfig.app.json, resolving TS2307 for @storybook/react-vite imports.
Replace 1x1 pixel PNG with a visible red/white checkerboard in the
ImagePreview story.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

clients/web/src/components/atoms/ContentViewer/ContentViewer.stories.tsx

@@ -28,7 +28,7 @@ export const ImagePreview: Story = {
   args: {
     type: "image",
     content:
-      "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mNk+M9QDwADhgGAWjR9awAAAABJRU5ErkJggg==",
+      "iVBORw0KGgoAAAANSUhEUgAAAGQAAABkCAYAAABw4pVUAAABWUlEQVR4nO3YsQnAMAwAQe+/dLKCRZpD+UA6cVh8p/Oc81z9t1/eJ+/oD/ybVxDMKwjmFQTzCoJ5BcG8gmBeQTCvIJg3mLQX2eIVBPMKgnkFwbyCYF5BMK8gmFcQzCsI5hUE8zqdYF5BMK8gmFcQzCsI5hUE8wqCeQXBvIJgXkEwbzBpL7LFKwjmFQTzCoJ5BcG8gmBeQTCvIJhXEMwrCOZ1OsG8gmBeQTCvIJhXEMwrCOYVBPMKgnkFwbyCYN5g0l5ki1cQzCsI5hUE8wqCeQXBvIJgXkEwryCYVxDM63SCeQXBvIJgXkEwryCYVxDMKwjmFQTzCoJ5BcG8waS9yBavIJhXEMwrCOYVBPMKgnkFwbyCYF5BMK8gmNfpBPMKgnkFwbyCYF5BMK8gmFcQzCsI5hUE8wqCeYNJe5EtXkEwryCYVxDMKwjmFQTzCoJ5BcG8gmBeQTDvBaFNwZ0T5gfxAAAAAElFTkSuQmCC",
     mimeType: "image/png",
   },
 };

clients/web/tsconfig.json

@@ -2,6 +2,7 @@
   "files": [],
   "references": [
     { "path": "./tsconfig.app.json" },
-    { "path": "./tsconfig.node.json" }
+    { "path": "./tsconfig.node.json" },
+    { "path": "./tsconfig.storybook.json" }
   ]
 }

clients/web/tsconfig.storybook.json

@@ -0,0 +1,8 @@
+{
+  "extends": "./tsconfig.app.json",
+  "compilerOptions": {
+    "types": ["vite/client"]
+  },
+  "include": ["src/**/*.stories.ts", "src/**/*.stories.tsx"],
+  "exclude": []
+}