feat(web): trim main nav; pair Discover+Requests; move chrome to user menu

The main nav was carrying surfaces that didn't belong on it:

- Search led to an empty page when clicked (you only ever want to land
  there from the global SearchInput typing into /search?q=...). Drop it.
- Requests is downstream of Discover (you discover, then you request).
  Lift both onto a shared horizontal tab strip; keep their URLs so
  bookmarks survive. New DiscoverTabs component used by both pages.
- Settings + Admin are operator chrome, not primary surfaces. Move them
  into the username dropdown alongside Log out, with Admin gated on
  is_admin. Users see Settings + Log out; admins see Settings + Admin
  + Log out.

Final main nav: Home / Artists / Albums / Liked / Discover / Playlists.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/src/lib/components/Shell.svelte

@@ -21,24 +21,17 @@
     return page.url.pathname.startsWith(href);
   }
 
+  // Search reaches /search via the global SearchInput in the header (not the
+  // nav). Requests is a tab inside Discover. Settings + Admin live in the
+  // username dropdown — they're per-operator chrome, not primary surfaces.
   const navItems = [
     { href: '/',                label: 'Home' },
     { href: '/library/artists', label: 'Artists' },
     { href: '/library/albums',  label: 'Albums' },
     { href: '/library/liked',   label: 'Liked' },
-    { href: '/search',          label: 'Search' },
     { href: '/discover',        label: 'Discover' },
-    { href: '/requests',        label: 'Requests' },
-    { href: '/playlists',       label: 'Playlists' },
-    { href: '/settings',        label: 'Settings' }
+    { href: '/playlists',       label: 'Playlists' }
   ];
-
-  // Admin link sits between Playlists and Settings, only visible to admins.
-  const visibleNavItems = $derived(
-    user.value?.is_admin
-      ? [...navItems.slice(0, -1), { href: '/admin', label: 'Admin' }, navItems[navItems.length - 1]]
-      : navItems
-  );
 </script>
 
 <svelte:window onclick={() => (menuOpen = false)} onkeydown={(e) => e.key === 'Escape' && (menuOpen = false)} />
@@ -59,15 +52,34 @@
       </button>
       {#if menuOpen}
         <div
-          class="absolute right-0 mt-1 w-32 rounded border border-border bg-surface shadow"
+          class="absolute right-0 mt-1 w-40 rounded border border-border bg-surface shadow"
           onclick={(e) => e.stopPropagation()}
           onkeydown={(e) => e.stopPropagation()}
           role="menu"
           tabindex="-1"
         >
+          <a
+            href="/settings"
+            role="menuitem"
+            class="block px-3 py-2 text-sm hover:bg-surface-hover"
+            onclick={() => (menuOpen = false)}
+          >
+            Settings
+          </a>
+          {#if user.value?.is_admin}
+            <a
+              href="/admin"
+              role="menuitem"
+              class="block px-3 py-2 text-sm hover:bg-surface-hover"
+              onclick={() => (menuOpen = false)}
+            >
+              Admin
+            </a>
+          {/if}
           <button
             type="button"
-            class="block w-full px-3 py-2 text-left hover:bg-surface-hover"
+            role="menuitem"
+            class="block w-full border-t border-border px-3 py-2 text-left text-sm hover:bg-surface-hover"
             onclick={handleLogout}
           >
             Log out
@@ -79,7 +91,7 @@
 
   <nav class="hidden w-48 border-r border-border bg-surface md:block">
     <ul class="p-2">
-      {#each visibleNavItems as item}
+      {#each navItems as item}
         <li>
           <a
             href={item.href}