feat: add wallet UI with 4 tabs and HomePage summary

- chain.js: API wrapper with Idempotency-Key auto-generation
- WalletPage: 4-tab container (wallet/assets/inventory/market)
- WalletTab: balance, address (truncated+copy), key export
- AssetsTab: asset list with detail expand, market listing
- InventoryTab: read-only slot display
- MarketTab: buy/cancel with confirm dialog, all/mine filter
- WalletSummary: HomePage card with balance + stats
- PrivateRoute guard for /wallet, header link on HomePage

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

src/api/chain.js

@@ -26,7 +26,7 @@ export async function exportWalletKey(password) {
   if (!res.ok) {
     const err = new Error(res.status === 401 ? '비밀번호가 올바르지 않습니다' : '키 내보내기에 실패했습니다');
     err.status = res.status;
-    try { const body = await res.json(); err.message = body.message || err.message; } catch {}
+    try { const body = await res.json(); err.message = body.message || err.message; } catch { /* ignore parse failure */ }
     throw err;
   }
   return res.json();