Add streaming haptic burst on first token arrival

Adds a multi-vibration "machine starting up" haptic pattern that fires
once when the first token of a response starts streaming in, similar to
ChatGPT's behavior. Uses navigator.vibrate([50, 30, 50, 30, 80]) for
three quick pulses that feel fun and responsive.

https://claude.ai/code/session_01Ewm55pEVHLfFzPHxmMyecw

Author: claude

src/lib/utils/haptics.ts

@@ -62,3 +62,11 @@ export function error() {
 export function selection() {
 	fire("selection");
 }
+
+/** Stream start burst — multiple short vibrations for a "machine starting up" feel. */
+export function streamStart(): void {
+	if (!enabled || !browser) return;
+	if (typeof navigator.vibrate !== "function") return;
+	// Three quick pulses: two short taps + a slightly longer finish
+	navigator.vibrate([50, 30, 50, 30, 80]);
+}

src/routes/conversation/[id]/+page.svelte

@@ -28,6 +28,7 @@
 	import { updateDebouncer } from "$lib/utils/updates.js";
 	import SubscribeModal from "$lib/components/SubscribeModal.svelte";
 	import { loading } from "$lib/stores/loading.js";
+	import { streamStart } from "$lib/utils/haptics";
 	import { requireAuthUser } from "$lib/utils/auth.js";
 	import { isConversationGenerationActive } from "$lib/utils/generationState";
 
@@ -320,6 +321,9 @@
 					) {
 						flushBuffer(currentTime);
 					}
+					if (pending) {
+						streamStart();
+					}
 					pending = false;
 				} else if (update.type === MessageUpdateType.FinalAnswer) {
 					// Mirror server-side merge behavior so the UI reflects the