fix(storybook): add base tag for /ui subpath URL resolution (#12)

The viteFinal config alone wasn't sufficient for subpath deployment.
Added <base href="/ui/"> to both manager-head.html and preview-head.html
to ensure all relative URLs resolve correctly.

Also fixed favicon path to be relative (works with base tag).

Fixes NEYN-8505

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: bob-obringer

.storybook/manager-head.html

@@ -1,3 +1,4 @@
+<base href="/ui/">
 <meta property="og:title" content="Neynar UI" />
 <meta property="og:description" content="AI-first React component library for coding agents. LLM-optimized docs, sensible defaults, zero config. Built on shadcn patterns, Base UI, and Tailwind CSS v4." />
 <meta property="og:image" content="https://neynar-ui.vercel.app/share-image.png" />
@@ -7,7 +8,7 @@
 <meta name="twitter:image" content="https://neynar-ui.vercel.app/share-image.png" />
 <meta name="twitter:site" content="@neynarxyz" />
 
-<link rel="icon" type="image/svg+xml" href="/neynar-logo.svg" />
+<link rel="icon" type="image/svg+xml" href="neynar-logo.svg" />
 
 <style>
   /* Hide the "Reset selection" option in toolbar dropdowns */

.storybook/preview-head.html

@@ -1,3 +1,4 @@
+<base href="/ui/">
 <style>
   /* MDX docs table styling - darker alternating rows for dark mode */
   .sbdocs-wrapper table tbody tr:nth-of-type(odd) {