Add zaps: NWC wallet connect + NIP-57 zap flow

- NWC client (nwc.ts): parse URI, encrypt/send kind 23194, await kind 23195 response
- Lightning store: persist NWC URI to localStorage, zap() via NDKZapper + lnPay callback
- ZapModal: amount presets (21/100/500/1000/5000 sats), custom amount, optional comment,
  paying/success/error states, prompts to Settings if no wallet connected
- ⚡ zap button on NoteCard (action row) and ProfileView (header, next to follow)
- Settings > Lightning Wallet section: paste NWC URI, connect/disconnect

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

src/lib/lightning/nwc.ts

@@ -0,0 +1,97 @@
+import NDK, { NDKEvent, NDKFilter, NDKKind, NDKPrivateKeySigner } from "@nostr-dev-kit/ndk";
+
+interface NwcConnection {
+  walletPubkey: string;
+  relayUrl: string;
+  secret: string;
+}
+
+export function parseNwcUri(uri: string): NwcConnection {
+  const cleaned = uri.replace("nostr+walletconnect://", "https://");
+  const url = new URL(cleaned);
+  const walletPubkey = url.hostname;
+  const relayUrl = url.searchParams.get("relay");
+  const secret = url.searchParams.get("secret");
+
+  if (!walletPubkey || !relayUrl || !secret) {
+    throw new Error("Invalid NWC URI: missing pubkey, relay, or secret");
+  }
+
+  return { walletPubkey, relayUrl, secret };
+}
+
+export function isValidNwcUri(uri: string): boolean {
+  try {
+    parseNwcUri(uri);
+    return uri.startsWith("nostr+walletconnect://");
+  } catch {
+    return false;
+  }
+}
+
+export async function payInvoiceViaNWC(nwcUri: string, bolt11: string): Promise<string> {
+  const { walletPubkey, relayUrl, secret } = parseNwcUri(nwcUri);
+
+  const ndk = new NDK({ explicitRelayUrls: [relayUrl] });
+  const signer = new NDKPrivateKeySigner(secret);
+  ndk.signer = signer;
+  await ndk.connect();
+
+  // Wait briefly for relay connection
+  await new Promise<void>((resolve) => {
+    const check = () => {
+      const relays = Array.from(ndk.pool?.relays?.values() ?? []);
+      if (relays.some((r) => r.connected)) resolve();
+      else setTimeout(check, 200);
+    };
+    setTimeout(() => resolve(), 8000); // timeout fallback
+    check();
+  });
+
+  const walletUser = ndk.getUser({ pubkey: walletPubkey });
+  const requestContent = JSON.stringify({
+    method: "pay_invoice",
+    params: { invoice: bolt11 },
+  });
+
+  const encrypted = await signer.encrypt(walletUser, requestContent, "nip04");
+
+  const requestEvent = new NDKEvent(ndk);
+  requestEvent.kind = NDKKind.NostrWalletConnectReq;
+  requestEvent.content = encrypted;
+  requestEvent.tags = [["p", walletPubkey]];
+  await requestEvent.sign();
+
+  return new Promise((resolve, reject) => {
+    const timeout = setTimeout(() => {
+      sub.stop();
+      reject(new Error("NWC payment timed out (30s)"));
+    }, 30000);
+
+    const filter: NDKFilter = {
+      kinds: [NDKKind.NostrWalletConnectRes],
+      authors: [walletPubkey],
+      "#e": [requestEvent.id!],
+    };
+
+    const sub = ndk.subscribe(filter, { closeOnEose: false });
+
+    sub.on("event", async (event: NDKEvent) => {
+      clearTimeout(timeout);
+      sub.stop();
+      try {
+        const decrypted = await signer.decrypt(walletUser, event.content, "nip04");
+        const response = JSON.parse(decrypted);
+        if (response.error) {
+          reject(new Error(response.error.message || "NWC payment failed"));
+        } else {
+          resolve(response.result?.preimage ?? "");
+        }
+      } catch (err) {
+        reject(err);
+      }
+    });
+
+    requestEvent.publish();
+  });
+}