Add Connect 4 multiplayer game server

Real-time two-player Connect 4 using Via framework with:
- Game creation and invite links
- SSE-based live updates for both players
- Win detection with animated highlighting
- Session-based nickname persistence

ui/lobby.go

@@ -0,0 +1,60 @@
+package ui
+
+import (
+	"github.com/ryanhamamura/via/h"
+)
+
+func LobbyView(nicknameBind, setNicknameKeyDown, createGameClick h.H) h.H {
+	return h.Main(h.Class("container"),
+		h.Div(h.Class("lobby"),
+			h.H1(h.Text("Connect 4")),
+			h.P(h.Text("Challenge a friend to a game of Connect 4!")),
+			h.Form(
+				h.FieldSet(
+					h.Label(h.Text("Your Nickname"), h.Attr("for", "nickname")),
+					h.Input(
+						h.ID("nickname"),
+						h.Type("text"),
+						h.Placeholder("Enter your nickname"),
+						nicknameBind,
+						h.Attr("required"),
+						setNicknameKeyDown,
+					),
+				),
+				h.Button(
+					h.Type("button"),
+					h.Text("Create Game"),
+					createGameClick,
+				),
+			),
+		),
+	)
+}
+
+func NicknamePrompt(nicknameBind, setNicknameKeyDown, setNicknameClick h.H) h.H {
+	return h.Main(h.Class("container"),
+		h.Div(h.Class("lobby"),
+			h.H1(h.Text("Join Game")),
+			h.P(h.Text("Enter your nickname to join the game.")),
+			h.Form(
+				h.FieldSet(
+					h.Label(h.Text("Your Nickname"), h.Attr("for", "nickname")),
+					h.Input(
+						h.ID("nickname"),
+						h.Type("text"),
+						h.Placeholder("Enter your nickname"),
+						nicknameBind,
+						h.Attr("required"),
+						h.Attr("autofocus"),
+						setNicknameKeyDown,
+					),
+				),
+				h.Button(
+					h.Type("button"),
+					h.Text("Join"),
+					setNicknameClick,
+				),
+			),
+		),
+	)
+}