Fix Windows socket WSAENOTCONN disconnect; add boss encounter frames

Socket fixes (fixes Windows-only connection failure):
- WorldSocket::connect() now waits for non-blocking connect to complete with
  select() before returning, preventing WSAENOTCONN on the first recv() call
  on Windows (Linux handles this implicitly but Windows requires writability
  poll after non-blocking connect)
- Add net::isConnectionClosed() helper: treats WSAENOTCONN/WSAECONNRESET/
  WSAESHUTDOWN/WSAECONNABORTED as graceful peer-close rather than recv errors
- Apply isConnectionClosed() in both WorldSocket and TCPSocket recv loops

UI:
- Add renderBossFrames(): displays boss unit health bars in top-right corner
  when SMSG_UPDATE_INSTANCE_ENCOUNTER_UNIT has active slots; supports
  click-to-target and color-coded health bars (red→orange→yellow as HP drops)

src/network/tcp_socket.cpp

@@ -153,6 +153,11 @@ void TCPSocket::update() {
         if (net::isWouldBlock(err)) {
             break;
         }
+        if (net::isConnectionClosed(err)) {
+            // Peer closed the connection — treat the same as recv() returning 0
+            sawClose = true;
+            break;
+        }
 
         LOG_ERROR("Receive failed: ", net::errorString(err));
         disconnect();

src/network/world_socket.cpp

@@ -128,6 +128,39 @@ bool WorldSocket::connect(const std::string& host, uint16_t port) {
             sockfd = INVALID_SOCK;
             return false;
         }
+
+        // Non-blocking connect in progress — wait up to 10s for completion.
+        // On Windows, calling recv() before the connect completes returns
+        // WSAENOTCONN; we must poll writability before declaring connected.
+        fd_set writefds, errfds;
+        FD_ZERO(&writefds);
+        FD_ZERO(&errfds);
+        FD_SET(sockfd, &writefds);
+        FD_SET(sockfd, &errfds);
+
+        struct timeval tv;
+        tv.tv_sec  = 10;
+        tv.tv_usec = 0;
+
+        int sel = ::select(static_cast<int>(sockfd) + 1, nullptr, &writefds, &errfds, &tv);
+        if (sel <= 0) {
+            LOG_ERROR("World server connection timed out (", host, ":", port, ")");
+            net::closeSocket(sockfd);
+            sockfd = INVALID_SOCK;
+            return false;
+        }
+
+        // Verify the socket error code — writeable doesn't guarantee success on all platforms
+        int sockErr = 0;
+        socklen_t errLen = sizeof(sockErr);
+        getsockopt(sockfd, SOL_SOCKET, SO_ERROR,
+                   reinterpret_cast<char*>(&sockErr), &errLen);
+        if (sockErr != 0) {
+            LOG_ERROR("Failed to connect to world server: ", net::errorString(sockErr));
+            net::closeSocket(sockfd);
+            sockfd = INVALID_SOCK;
+            return false;
+        }
     }
 
     connected = true;
@@ -369,6 +402,11 @@ void WorldSocket::update() {
         if (net::isWouldBlock(err)) {
             break;
         }
+        if (net::isConnectionClosed(err)) {
+            // Peer closed the connection — treat the same as recv() returning 0
+            sawClose = true;
+            break;
+        }
 
         LOG_ERROR("Receive failed: ", net::errorString(err));
         disconnect();