fix: hide logout button when not authenticated (#465)

The logout button was rendered outside the isAuthenticated check,
causing both login and logout buttons to appear on desktop when
logged out.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

authored by zzstoatzz.io Claude and committed by GitHub 45feff7c e8020fab

Changed files
+5 -3
frontend
src
lib
components
+5 -3
frontend/src/lib/components/Header.svelte
··· 27 <SearchTrigger /> 28 </div> 29 <!-- Logout positioned on far right, mirroring stats --> 30 - <div class="logout-right desktop-only"> 31 - <button onclick={onLogout} class="btn-logout-outer" title="log out">logout</button> 32 - </div> 33 <div class="header-content"> 34 <div class="left-section"> 35 <!-- desktop: show icons inline -->
··· 27 <SearchTrigger /> 28 </div> 29 <!-- Logout positioned on far right, mirroring stats --> 30 + {#if isAuthenticated} 31 + <div class="logout-right desktop-only"> 32 + <button onclick={onLogout} class="btn-logout-outer" title="log out">logout</button> 33 + </div> 34 + {/if} 35 <div class="header-content"> 36 <div class="left-section"> 37 <!-- desktop: show icons inline -->