feat(chat): CLI flags, centered header; improve server with selective broadcast and quit handling

Client/main:
- Add flags: -host (default "localhost:9000") and -server (run only server)
- When -server is set, startTCPServer(host) and exit
- Use provided host for client connection
- Center header with width-aware lipgloss styling; adjust padding

Server:
- Introduce broadcast struct {text string, exclude net.Conn}
- Hub.msgCh now chan broadcast; send messages with optional exclusion
- On join: send “[join] …” to others (exclude the joiner)
- Broadcast chat lines without exclusion; newline-delimited as before
- Handle “/quit” by breaking loop (graceful disconnect)
- On leave: broadcast “[leave] …” to all

Refactor notes:
- Remove unconditional embedded server from client startup
- Scanner loop unchanged aside from quit handling and broadcast usage

main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"bufio"
 	"errors"
+	"flag"
 	"fmt"
 	"io"
 	"net"
@@ -179,7 +180,7 @@ func (m *model) refreshViewport() {
 }
 
 func (m model) View() string {
-	header := lipgloss.NewStyle().Foreground(lipgloss.Color("241")).Bold(true).Render(m.server)
+	header := lipgloss.NewStyle().Width(m.vp.Width).Padding(0, 1).Align(lipgloss.Center).Foreground(lipgloss.Color("241")).Bold(true).Render(m.server)
 	return lipgloss.JoinVertical(
 		lipgloss.Left,
 		header,
@@ -189,15 +190,25 @@ func (m model) View() string {
 }
 
 func main() {
-	go func() {
-		if err := startTCPServer("localhost:9000"); err != nil {
+	var (
+		host       string
+		serverOnly bool
+	)
+
+	flag.StringVar(&host, "host", "localhost:9000", "host:port to connect to or bind the server on")
+	flag.BoolVar(&serverOnly, "server", false, "run only the server")
+	flag.Parse()
+
+	if serverOnly {
+		if err := startTCPServer(host); err != nil {
 			fmt.Println("Server error:", err)
 		}
-	}()
+		return
+	}
 
 	time.Sleep(200 * time.Millisecond)
 
-	p := tea.NewProgram(initialModel("127.0.0.1:9000"), tea.WithAltScreen(), tea.WithMouseCellMotion())
+	p := tea.NewProgram(initialModel(host), tea.WithAltScreen(), tea.WithMouseCellMotion())
 	if _, err := p.Run(); err != nil {
 		fmt.Println("Error:", err)
 	}

server.go

@@ -9,12 +9,17 @@ import (
 	"sync"
 )
 
+type broadcast struct {
+	text    string
+	exclude net.Conn
+}
+
 type Hub struct {
 	mu      sync.Mutex
 	conns   map[net.Conn]struct{}
 	joinCh  chan net.Conn
 	leaveCh chan net.Conn
-	msgCh   chan string
+	msgCh   chan broadcast
 }
 
 func NewHub() *Hub {
@@ -22,7 +27,7 @@ func NewHub() *Hub {
 		conns:   make(map[net.Conn]struct{}),
 		joinCh:  make(chan net.Conn),
 		leaveCh: make(chan net.Conn),
-		msgCh:   make(chan string, 128),
+		msgCh:   make(chan broadcast, 128),
 	}
 }
 
@@ -43,8 +48,10 @@ func (h *Hub) Run() {
 		case msg := <-h.msgCh:
 			h.mu.Lock()
 			for c := range h.conns {
-				// newline-delimited messages
-				fmt.Fprintln(c, msg)
+				if msg.exclude != nil && c == msg.exclude {
+					continue
+				}
+				fmt.Fprintln(c, msg.text)
 			}
 			h.mu.Unlock()
 		}
@@ -57,7 +64,7 @@ func handleConn(h *Hub, c net.Conn) {
 
 	name := c.RemoteAddr().String()
 	fmt.Fprintf(c, "Welcome %s\n", name)
-	h.msgCh <- fmt.Sprintf("[join] %s", name)
+	h.msgCh <- broadcast{text: fmt.Sprintf("[join] %s", name), exclude: c}
 
 	scanner := bufio.NewScanner(c)
 	scanner.Buffer(make([]byte, 0, 1024), 64*1024)
@@ -67,14 +74,14 @@ func handleConn(h *Hub, c net.Conn) {
 			continue
 		}
 		if line == "/quit" {
-			return
+			break
 		}
-		h.msgCh <- fmt.Sprintf("%s: %s", name, line)
+		h.msgCh <- broadcast{text: fmt.Sprintf("%s: %s", name, line)}
 	}
 	if err := scanner.Err(); err != nil {
 		log.Printf("read err from %s: %v", name, err)
 	}
-	h.msgCh <- fmt.Sprintf("[leave] %s", name)
+	h.msgCh <- broadcast{text: fmt.Sprintf("[leave] %s", name)}
 }
 
 func startTCPServer(addr string) error {