Add zap history view (roadmap #9)

- fetchZapsReceived: kind 9735 filtered by #p tag (receipts)
- fetchZapsSent: kind 9734 filtered by authors (zap requests)
- ZapHistoryView: Received / Sent tabs with row count; header shows
  total sats in/out; each row: avatar, amount, counterpart name
  (clickable → profile), comment, time ago
- Receipt parsing: amount from embedded zap request in "description"
  tag (millisats → sats); sender from uppercase "P" tag with fallback
  to zap request pubkey
- Request parsing: amount from "amount" tag, recipient from "p" tag
- ⚡ zaps nav item added to sidebar between search and relays
- Logged-out fallback state with prompt to log in

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

src/components/sidebar/Sidebar.tsx

@@ -7,6 +7,7 @@ import { AccountSwitcher } from "./AccountSwitcher";
 const NAV_ITEMS = [
   { id: "feed" as const, label: "feed", icon: "◈" },
   { id: "search" as const, label: "search", icon: "⌕" },
+  { id: "zaps" as const, label: "zaps", icon: "⚡" },
   { id: "relays" as const, label: "relays", icon: "⟐" },
   { id: "settings" as const, label: "settings", icon: "⚙" },
   { id: "about" as const, label: "support", icon: "♥" },