feat(chat): colorize usernames by ID; refine IDs/usernames and /name parsing

Server:
- Generate 6-char IDs from lowercase hex alphabet "abcdef0123456789"
- Default username now uses the ID as-is (no extra ToLower)
- Use strings.CutPrefix for robust “/name ” command parsing

Client:
- Add colorizeLine to apply ANSI colors based on 6-hex-digit ID
  - Colorize chat lines: "<name> (<id>): <msg>"
  - Colorize [join]/[leave] notices
  - Colorize [rename] events
  - Colorize Welcome banner
- Apply colorizeLine to incoming netMsg before appending

Notes:
- ID regex patterns accept 6 hex digits (case-insensitive), rendered in lowercase
- Keeps non-matching lines unchanged

main.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"io"
 	"net"
+	"regexp"
 	"strings"
 	"time"
 
@@ -16,6 +17,45 @@ import (
 	"github.com/charmbracelet/lipgloss"
 )
 
+// colorizeLine applies ANSI styling to usernames based on 6-hex-digit id from the server.
+func colorizeLine(s string) string {
+	reChat := regexp.MustCompile(`^(.+?) \(([0-9a-fA-F]{6})\):[ \t]*(.*)$`)
+	if m := reChat.FindStringSubmatch(s); m != nil {
+		id := strings.ToLower(m[2])
+		nameStyle := lipgloss.NewStyle().Foreground(lipgloss.Color("#" + id)).Bold(true)
+		name := nameStyle.Render(m[1])
+		rest := strings.TrimSpace(m[3])
+		return fmt.Sprintf("%s (%s): %s", name, id, rest)
+	}
+
+	reJoinLeave := regexp.MustCompile(`^\[(join|leave)\] (.+?) \(([0-9a-fA-F]{6})\)$`)
+	if m := reJoinLeave.FindStringSubmatch(s); m != nil {
+		id := strings.ToLower(m[3])
+		nameStyle := lipgloss.NewStyle().Foreground(lipgloss.Color("#" + id)).Bold(true)
+		uname := nameStyle.Render(m[2])
+		return fmt.Sprintf("[%s] %s (%s)", m[1], uname, id)
+	}
+
+	reRename := regexp.MustCompile(`^\[rename\] (.+?) \(([0-9a-fA-F]{6})\) -> (.+)$`)
+	if m := reRename.FindStringSubmatch(s); m != nil {
+		id := strings.ToLower(m[2])
+		nameStyle := lipgloss.NewStyle().Foreground(lipgloss.Color("#" + id)).Bold(true)
+		oldN := nameStyle.Render(m[1])
+		newN := nameStyle.Render(m[3])
+		return fmt.Sprintf("[rename] %s (%s) -> %s", oldN, id, newN)
+	}
+
+	reWelcome := regexp.MustCompile(`^Welcome (.+?) \(([0-9a-fA-F]{6})\)$`)
+	if m := reWelcome.FindStringSubmatch(s); m != nil {
+		id := strings.ToLower(m[2])
+		nameStyle := lipgloss.NewStyle().Foreground(lipgloss.Color("#" + id)).Bold(true)
+		uname := nameStyle.Render(m[1])
+		return fmt.Sprintf("Welcome %s (%s)", uname, id)
+	}
+
+	return s
+}
+
 type netMsg string
 type connectedMsg struct{ conn net.Conn }
 type disconnectedMsg struct{}
@@ -122,7 +162,7 @@ func (m model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 		return m, nil
 
 	case netMsg:
-		m.messages = append(m.messages, string(msg))
+		m.messages = append(m.messages, colorizeLine(string(msg)))
 		m.refreshViewport()
 
 		if m.conn != nil && !strings.HasPrefix(string(msg), "[error] read") {

server.go

@@ -102,14 +102,14 @@ func handleConn(h *Hub, c net.Conn) {
 	h.joinCh <- c
 
 	// Generate per-connection ID
-	id, err := gonanoid.Generate("ABCDEF0123456789", 6)
+	id, err := gonanoid.Generate("abcdef0123456789", 6)
 	if err != nil || id == "" {
 		// Fallback to remote addr if generation fails
 		id = c.RemoteAddr().String()
 	}
 
 	// Default username is server-controlled; not necessarily unique
-	defaultName := "user_" + strings.ToLower(id)
+	defaultName := "user_" + id
 	username := defaultName
 
 	// Greet client and instruct on setting username
@@ -132,8 +132,7 @@ func handleConn(h *Hub, c net.Conn) {
 		if line == "/quit" {
 			break // unified leave handling below
 		}
-		if strings.HasPrefix(line, "/name ") {
-			desired := strings.TrimSpace(strings.TrimPrefix(line, "/name "))
+		if desired, ok := strings.CutPrefix(line, "/name "); ok {
 			newName := sanitizeUsername(desired)
 			if newName == "" {
 				fmt.Fprintln(c, "[error] invalid username")