refactor: patch connection indicator with timestamp

Server patches the ConnectionIndicator element with a timestamp on
each heartbeat. Client-side JS checks every second if the timestamp
is stale (>20s) and toggles red/green accordingly.

This properly detects connection loss since the indicator will turn
red if no patches are received.

features/c4game/pages/game.templ

@@ -15,10 +15,10 @@ templ GamePage(g *connect4.Game, myColor int, messages []chat.Message, chatCfg c
 	@layouts.Base("Connect 4") {
 		<main
 			class="flex flex-col items-center gap-4 p-4"
-			data-signals="{chatMsg: '', lastPing: 0}"
+			data-signals="{chatMsg: ''}"
 			data-init={ fmt.Sprintf("@get('/games/%s/events',{requestCancellation:'disabled'})", g.ID) }
 		>
-			@sharedcomponents.ConnectionIndicator()
+			@sharedcomponents.ConnectionIndicator(0)
 			@GameContent(g, myColor, messages, chatCfg)
 		</main>
 	}