feat: add BTC ↔ Lightning swaps via Boltz Exchange

- New Boltz API client (lib/swap/boltz.ts) - no API key needed
- API routes: /api/swap/boltz (create/estimate) and /api/swap/boltz/[id] (status)
- BoltzSwap UI component in web wallet swap tab
- Supports both directions:
  - BTC → Lightning (submarine swap): creates LN invoice, gets BTC deposit address
  - Lightning → BTC (reverse swap): pays LN invoice, receives on-chain BTC
- Live fee estimates, swap status polling, copy-to-clipboard
- Non-custodial via Boltz public API

Author: ralyodio

src/app/api/swap/boltz/[id]/route.ts

@@ -0,0 +1,21 @@
+/**
+ * GET /api/swap/boltz/[id] - Check Boltz swap status
+ */
+import { NextRequest, NextResponse } from 'next/server';
+import { getSwapStatus } from '@/lib/swap/boltz';
+
+export async function GET(
+  request: NextRequest,
+  { params }: { params: Promise<{ id: string }> },
+) {
+  try {
+    const { id } = await params;
+    const status = await getSwapStatus(id);
+    return NextResponse.json({ success: true, ...status });
+  } catch (error) {
+    return NextResponse.json(
+      { success: false, error: error instanceof Error ? error.message : 'Failed to get swap status' },
+      { status: 500 },
+    );
+  }
+}

src/app/api/swap/boltz/route.ts

@@ -0,0 +1,69 @@
+/**
+ * GET /api/swap/boltz - Get Boltz pair info (limits, fees)
+ * POST /api/swap/boltz - Create a BTC ↔ Lightning swap
+ */
+import { NextRequest, NextResponse } from 'next/server';
+import {
+  getBoltzPairInfo,
+  createSwapIn,
+  createSwapOut,
+  estimateSwapFee,
+} from '@/lib/swap/boltz';
+
+export async function GET() {
+  try {
+    const pair = await getBoltzPairInfo();
+    return NextResponse.json({ success: true, pair });
+  } catch (error) {
+    return NextResponse.json(
+      { success: false, error: error instanceof Error ? error.message : 'Failed to get pair info' },
+      { status: 500 },
+    );
+  }
+}
+
+export async function POST(request: NextRequest) {
+  try {
+    const body = await request.json();
+    const { direction, invoice, refundAddress, amountSats, claimAddress } = body;
+
+    if (direction === 'in') {
+      // On-chain BTC → Lightning
+      if (!invoice) {
+        return NextResponse.json({ success: false, error: 'Lightning invoice required' }, { status: 400 });
+      }
+      const swap = await createSwapIn(invoice, refundAddress);
+      return NextResponse.json({ success: true, swap });
+    } else if (direction === 'out') {
+      // Lightning → On-chain BTC
+      if (!amountSats || !claimAddress) {
+        return NextResponse.json(
+          { success: false, error: 'amountSats and claimAddress required' },
+          { status: 400 },
+        );
+      }
+      const swap = await createSwapOut(amountSats, claimAddress);
+      return NextResponse.json({ success: true, swap });
+    } else if (direction === 'estimate') {
+      // Fee estimation
+      if (!amountSats || !body.swapDirection) {
+        return NextResponse.json(
+          { success: false, error: 'amountSats and swapDirection (in/out) required' },
+          { status: 400 },
+        );
+      }
+      const estimate = await estimateSwapFee(body.swapDirection, amountSats);
+      return NextResponse.json({ success: true, estimate });
+    } else {
+      return NextResponse.json(
+        { success: false, error: 'direction must be "in", "out", or "estimate"' },
+        { status: 400 },
+      );
+    }
+  } catch (error) {
+    return NextResponse.json(
+      { success: false, error: error instanceof Error ? error.message : 'Swap failed' },
+      { status: 500 },
+    );
+  }
+}

src/app/web-wallet/page.tsx

@@ -13,6 +13,7 @@ import {
 } from '@/components/web-wallet/TransactionList';
 import { SwapForm } from '@/components/web-wallet/SwapForm';
 import { SwapHistory, PendingSwaps } from '@/components/web-wallet/SwapHistory';
+import { BoltzSwap } from '@/components/web-wallet/BoltzSwap';
 import type { WalletChain } from '@/lib/web-wallet/identity';
 
 export default function WebWalletPage() {
@@ -328,6 +329,14 @@ function DashboardView() {
               {/* Pending Swaps */}
               <PendingSwaps walletId={walletId} />
 
+              {/* BTC ↔ Lightning Swap */}
+              <BoltzSwap
+                walletId={walletId}
+                btcAddress={addressMap["BTC"]}
+                btcBalance={balanceMap["BTC"]?.balance}
+                lnBalance={balanceMap["LN"]?.balance}
+              />
+
               {/* New Swap Form */}
               <div>
                 <div className="mb-4">