Keep desktop UI icon previews aligned with the packaged app icon

The desktop UI was still rendering the old JPG preview asset, so the empty
state, sidebar, and settings pages continued to show the legacy glow-backed
image even after the packaged app icon was corrected. This switches those UI
surfaces to a PNG generated from the current canonical app icon source so the
in-app preview matches the shipped icon treatment.

Constraint: The desktop UI still referenced a legacy JPG asset with the removed outer glow background
Constraint: There are unrelated staged changes in the worktree, so this commit must stay file-scoped
Rejected: Leave the UI on the JPG asset | keeps showing a stale icon treatment after the packaging fix
Rejected: Revert the packaged icon to match the old JPG | would reintroduce the original square-background problem
Confidence: high
Scope-risk: narrow
Reversibility: clean
Directive: Keep desktop/public/app-icon.png in sync with desktop/src-tauri/app-icon.svg when the app icon changes
Tested: desktop bun run lint; desktop bun run test
Not-tested: Manual visual pass in the running desktop app after rebuilding the frontend bundle

desktop/src/components/layout/Sidebar.tsx

@@ -125,7 +125,7 @@ export function Sidebar() {
       <div className={`px-3 pb-2 ${isTauri && !isWindows ? 'pt-[44px]' : 'pt-3'}`}>
         <div className={`flex ${sidebarOpen ? 'items-center justify-between gap-3' : 'flex-col items-center gap-2'}`}>
           <div className={`flex min-w-0 items-center ${sidebarOpen ? 'gap-2.5' : 'justify-center'}`}>
-            <img src="/app-icon.jpg" alt="" className="h-8 w-8 rounded-lg flex-shrink-0" />
+            <img src="/app-icon.png" alt="" className="h-8 w-8 rounded-lg flex-shrink-0" />
             <span
               className={`sidebar-copy ${sidebarOpen ? 'sidebar-copy--visible' : 'sidebar-copy--hidden'} text-[13px] font-semibold tracking-tight text-[var(--color-text-primary)]`}
               style={{ fontFamily: 'var(--font-headline)' }}

desktop/src/pages/ActiveSession.tsx

@@ -141,7 +141,7 @@ export function ActiveSession() {
               </>
             ) : (
               <>
-                <img src="/app-icon.jpg" alt="Claude Code Haha" className="mb-6 h-24 w-24 rounded-[22px]" style={{ boxShadow: 'var(--shadow-dropdown)' }} />
+                <img src="/app-icon.png" alt="Claude Code Haha" className="mb-6 h-24 w-24 rounded-[22px]" style={{ boxShadow: 'var(--shadow-dropdown)' }} />
                 <h1 className="mb-2 text-3xl font-extrabold tracking-tight text-[var(--color-text-primary)]" style={{ fontFamily: 'var(--font-headline)' }}>
                   {t('empty.title')}
                 </h1>

desktop/src/pages/EmptySession.tsx

@@ -374,7 +374,7 @@ export function EmptySession() {
     <div className="relative flex flex-1 flex-col overflow-hidden bg-[var(--color-surface)]">
       <div className="flex flex-1 flex-col items-center justify-center p-8 pb-32">
         <div className="flex max-w-md flex-col items-center text-center">
-          <img src="/app-icon.jpg" alt="Claude Code Haha" className="mb-6 h-24 w-24 rounded-[22px]" style={{ boxShadow: 'var(--shadow-dropdown)' }} />
+          <img src="/app-icon.png" alt="Claude Code Haha" className="mb-6 h-24 w-24 rounded-[22px]" style={{ boxShadow: 'var(--shadow-dropdown)' }} />
           <h1 className="mb-2 text-3xl font-extrabold tracking-tight text-[var(--color-text-primary)]" style={{ fontFamily: 'var(--font-headline)' }}>
             {t('empty.title')}
           </h1>

desktop/src/pages/Settings.tsx

@@ -1332,7 +1332,7 @@ function AboutSettings() {
   return (
     <div className="w-full min-w-0 max-w-lg mx-auto flex flex-col items-center py-6">
       {/* Logo + App Name + Version */}
-      <img src="/app-icon.jpg" alt="Claude Code Haha" className="w-20 h-20 rounded-2xl shadow-md mb-4" />
+      <img src="/app-icon.png" alt="Claude Code Haha" className="w-20 h-20 rounded-2xl shadow-md mb-4" />
       <h1 className="text-xl font-bold text-[var(--color-text-primary)]">Claude Code Haha</h1>
       {version && (
         <span className="text-xs text-[var(--color-text-tertiary)] mt-1">{t('settings.about.version')} {version}</span>