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/routes/discover/+page.svelte

@@ -2,6 +2,7 @@
   import { createLidarrSearchQuery } from '$lib/api/lidarr';
   import { createRequest } from '$lib/api/requests';
   import DiscoverResultCard from '$lib/components/DiscoverResultCard.svelte';
+  import DiscoverTabs from '$lib/components/DiscoverTabs.svelte';
   import ApiErrorBanner from '$lib/components/ApiErrorBanner.svelte';
   import SuggestionFeed from '$lib/components/SuggestionFeed.svelte';
   import type {
@@ -114,7 +115,9 @@
   ];
 </script>
 
-<div class="space-y-6">
+<DiscoverTabs />
+
+<div class="space-y-6 pt-6">
   <input
     type="search"
     aria-label="Search Lidarr"

web/src/routes/requests/+page.svelte

@@ -5,6 +5,7 @@
   import { qk } from '$lib/api/queries';
   import StatusPill from '$lib/components/StatusPill.svelte';
   import ApiErrorBanner from '$lib/components/ApiErrorBanner.svelte';
+  import DiscoverTabs from '$lib/components/DiscoverTabs.svelte';
   import type { LidarrRequest, LidarrRequestKind } from '$lib/api/types';
 
   const queryStore = createMyRequestsQuery();
@@ -60,7 +61,9 @@
   }
 </script>
 
-<div class="space-y-6">
+<DiscoverTabs />
+
+<div class="space-y-6 pt-6">
   <header class="space-y-1">
     <h2 class="font-display text-2xl font-medium text-text-primary">
       Your requests