feat: add Solana USDT/USDC support and refine admin payouts UI

app/api/merchants/[id]/balances/route.ts

@@ -0,0 +1,34 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { db } from '@/lib/db';
+
+export async function GET(
+    req: NextRequest,
+    context: { params: Promise<{ id: string }> }
+) {
+    try {
+        const { id } = await context.params;
+
+        const result = await db.query(
+            'SELECT network, token, balance, withdrawn, total_gross FROM merchant_balances WHERE merchant_id = $1 ORDER BY network, token',
+            [id]
+        );
+
+        // Also get the merchant fee
+        const merchantRes = await db.query('SELECT fee_percent FROM merchants WHERE id = $1', [id]);
+        const feePercent = parseFloat(merchantRes.rows[0]?.fee_percent || '1.0');
+
+        return NextResponse.json({
+            balances: result.rows.map(r => ({
+                network: r.network,
+                token: r.token,
+                balance: parseFloat(r.balance),
+                withdrawn: parseFloat(r.withdrawn),
+                totalGross: parseFloat(r.total_gross || r.balance),
+                available: parseFloat(r.balance) - parseFloat(r.withdrawn)
+            })),
+            feePercent
+        });
+    } catch (err: any) {
+        return NextResponse.json({ error: err.message }, { status: 500 });
+    }
+}