feat: disable recharge modal, show coming-soon toast instead

Payment gateway is not yet configured, so hide the recharge flow
and show an informational toast when users click the balance button.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/components/AppShell.tsx

@@ -370,7 +370,7 @@ function AppShell({
                 className="member-button"
                 type="button"
                 aria-label={`积分余额 ${displayedBalanceLabel}`}
-                onClick={() => setRechargeOpen(true)}
+                onClick={() => toast.info("充值功能即将开放，敬请期待")}
               >
                 <WalletOutlined />
                 <span className="member-button__label">{displayedBalanceLabel}</span>