fix(desktop): resolve renderer assets relative to BASE_URL

Absolute public asset paths (/apple-touch-icon.png, /ds-assets/...) work
under the dev server but break in the packaged app, where the renderer is
loaded from file://.../index.html and a leading slash resolves to the
filesystem root -> broken onboarding provider icon and backdrop image on
macOS. Prefix these with import.meta.env.BASE_URL so they resolve next to
the bundled index.html in both dev and packaged builds.

apps/desktop/src/components/Backdrop.tsx

@@ -21,6 +21,7 @@ const BLEND_MODES = [
 ] as const
 
 type BlendMode = (typeof BLEND_MODES)[number]
+const assetPath = (path: string) => `${import.meta.env.BASE_URL}${path.replace(/^\/+/, '')}`
 
 export function Backdrop() {
   const [controlsOpen, setControlsOpen] = useState(false)
@@ -99,7 +100,7 @@ export function Backdrop() {
             alt=""
             className="w-auto min-w-dvw object-cover"
             fetchPriority="low"
-            src="/ds-assets/filler-bg0.jpg"
+            src={assetPath('ds-assets/filler-bg0.jpg')}
             style={{
               height: `${statue.scale}dvh`,
               objectPosition: statue.objectPosition,

apps/desktop/src/components/desktop-onboarding-overlay.tsx

@@ -108,6 +108,8 @@ const PROVIDER_DISPLAY: Record<string, { order: number; title: string }> = {
   'qwen-oauth': { order: 5, title: 'Qwen Code' }
 }
 
+const assetPath = (path: string) => `${import.meta.env.BASE_URL}${path.replace(/^\/+/, '')}`
+
 const FLOW_SUBTITLES: Record<OAuthProvider['flow'], string> = {
   pkce: 'Opens your browser to sign in, then continues here',
   device_code: 'Opens a verification page in your browser — Hermes connects automatically',
@@ -333,7 +335,7 @@ function FeaturedProviderRow({
     >
       <div className="min-w-0">
         <div className="flex items-center gap-2">
-          <img alt="" className="size-5 shrink-0 rounded" src="/apple-touch-icon.png" />
+          <img alt="" className="size-5 shrink-0 rounded" src={assetPath('apple-touch-icon.png')} />
           <span className="text-base font-semibold">{providerTitle(provider)}</span>
           {loggedIn ? (
             <ConnectedTag />