Add search view (NIP-50 + hashtag + people)

- searchNotes: NIP-50 full-text for text queries, #t tag filter for #hashtags
- searchUsers: NIP-50 kind 0 search for people
- SearchView with tabbed notes/people results, follow/unfollow inline
- Hashtag queries skip people search and use universal #t filter
- Graceful empty state explains NIP-50 relay support caveat
- Search added to sidebar nav (⌕)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/components/sidebar/Sidebar.tsx

@@ -7,6 +7,7 @@ import { shortenPubkey } from "../../lib/utils";
 
 const NAV_ITEMS = [
   { id: "feed" as const, label: "feed", icon: "◈" },
+  { id: "search" as const, label: "search", icon: "⌕" },
   { id: "relays" as const, label: "relays", icon: "⟐" },
   { id: "settings" as const, label: "settings", icon: "⚙" },
 ] as const;