Add About / Support page (roadmap #4)

- New 'about' view wired into sidebar nav (♥ support) and App.tsx
- Sections: in-app zap button (reuses ZapModal + NWC infra), Lightning
  address QR + copy, Bitcoin address QR + copy, Ko-fi link, GitHub link,
  version/tech credits footer
- QR codes rendered as SVG via react-qr-code (no canvas dependency)
- lightning: URI and bitcoin: URI formats for wallet-scannable QR codes
- Tasteful and non-nagging — lives in the nav, never pops up unprompted

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

src/components/sidebar/Sidebar.tsx

@@ -9,6 +9,7 @@ const NAV_ITEMS = [
   { id: "search" as const, label: "search", icon: "⌕" },
   { id: "relays" as const, label: "relays", icon: "⟐" },
   { id: "settings" as const, label: "settings", icon: "⚙" },
+  { id: "about" as const, label: "support", icon: "♥" },
 ] as const;
 
 export function Sidebar() {