feat: Implement NIP-07 visitor identity in the Workshop

- Add 'Connect Nostr' button and display npub in the Workshop header.
- Implement NIP-07 detection and connect flow.
- Store and retrieve npub from localStorage.
- Implement disconnect functionality.
- Include visitor's npub in WebSocket presence events.
- Implement fallback UI for missing NIP-07 extension.
- Update Timmy greeting logic to use npub.

Fixes #14

artifacts/api-server/src/routes/events.ts

@@ -38,6 +38,9 @@ const logger = makeLogger("ws-events");
 
 const PING_INTERVAL_MS = 30_000;
 
+// Map to store visitorId -> npub mappings
+const connectedVisitors = new Map<string, string>();
+
 // ── Per-visitor rate limit (3 replies/minute) ─────────────────────────────────
 const CHAT_RATE_LIMIT = 3;
 const CHAT_RATE_WINDOW_MS = 60_000;
@@ -323,12 +326,19 @@ export function attachWebSocketServer(server: Server): void {
 
     socket.on("message", (raw) => {
       try {
-        const msg = JSON.parse(raw.toString()) as { type?: string; text?: string; visitorId?: string };
+        const msg = JSON.parse(raw.toString()) as { type?: string; text?: string; visitorId?: string; npub?: string };
         if (msg.type === "pong") return;
         if (msg.type === "subscribe") {
           send(socket, { type: "agent_count", count: wss.clients.size });
         }
         if (msg.type === "visitor_enter") {
+          const { visitorId, npub } = msg;
+          if (visitorId && npub) {
+            connectedVisitors.set(visitorId, npub);
+            const formattedNpub = `${npub.slice(0, 8)}…${npub.slice(-4)}`;
+            broadcastToAll(wss, { type: "chat", agentId: "timmy", text: `Welcome, Nostr user ${formattedNpub}! What can I help you with?` });
+          }
+
           wss.clients.forEach(c => {
             if (c !== socket && c.readyState === 1) {
               c.send(JSON.stringify({ type: "visitor_count", count: wss.clients.size }));
@@ -337,6 +347,10 @@ export function attachWebSocketServer(server: Server): void {
           send(socket, { type: "visitor_count", count: wss.clients.size });
         }
         if (msg.type === "visitor_leave") {
+          const { visitorId } = msg;
+          if (visitorId) {
+            connectedVisitors.delete(visitorId);
+          }
           wss.clients.forEach(c => {
             if (c !== socket && c.readyState === 1) {
               c.send(JSON.stringify({ type: "visitor_count", count: Math.max(0, wss.clients.size - 1) }));