docs: update `$effect` examples (#15463)

* docs: update effect examples

* revert

* Update documentation/docs/02-runes/04-$effect.md

* update example

* revert

* update effect root example

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>

documentation/docs/02-runes/04-$effect.md

@@ -25,7 +25,7 @@ You can create an effect with the `$effect` rune ([demo](/playground/untitled#H4
 	});
 </script>
 
-<canvas bind:this={canvas} width="100" height="100" />
+<canvas bind:this={canvas} width="100" height="100"></canvas>
 ```
 
 When Svelte runs an effect function, it tracks which pieces of state (and derived state) are accessed (unless accessed inside [`untrack`](svelte#untrack)), and re-runs the function when that state later changes.
@@ -135,19 +135,33 @@ An effect only reruns when the object it reads changes, not when a property insi
 
 An effect only depends on the values that it read the last time it ran. This has interesting implications for effects that have conditional code.
 
-For instance, if `a` is `true` in the code snippet below, the code inside the `if` block will run and `b` will be evaluated. As such, changes to either `a` or `b` [will cause the effect to re-run](/playground/untitled#H4sIAAAAAAAAE3VQzWrDMAx-FdUU4kBp71li6EPstOxge0ox8-QQK2PD-N1nLy2F0Z2Evj9_chKkP1B04pnYscc3cRCT8xhF95IEf8-Vq0DBr8rzPB_jJ3qumNERH-E2ECNxiRF9tIubWY00lgcYNAywj6wZJS8rtk83wjwgCrXHaULLUrYwKEgVGrnkx-Dx6MNFNstK5OjSbFGbwE0gdXuT_zGYrjmAuco515Hr1p_uXak3K3MgCGS9s-9D2grU-judlQYXIencnzad-tdR79qZrMyvw9wd5Z8Yv1h09dz8mn8AkM7Pfo0BAAA=).
+For instance, if `condition` is `true` in the code snippet below, the code inside the `if` block will run and `color` will be evaluated. As such, changes to either `condition` or `color` [will cause the effect to re-run](/playground/untitled#H4sIAAAAAAAAE21RQW6DMBD8ytaNBJHaJFLViwNIVZ8RcnBgXVk1xsILTYT4e20TQg89IOPZ2fHM7siMaJBx9tmaWpFqjQNlAKXEihx7YVJpdIyfRkY3G4gB8Pi97cPanRtQU8AuwuF_eNUaQuPlOMtc1SlLRWlKUo1tOwJflUikQHZtA0klzCDc64Imx0ANn8bInV1CDhtHgjClrsftcSXotluLybOUb3g4JJHhOZs5WZpuIS9gjNqkJKQP5e2ClrR4SMdZ13E4xZ8zTPOTJU2A2uE_PQ9COCI926_hTVarIU4hu_REPlBrKq2q73ycrf1N-vS4TMUsulaVg3EtR8H9rFgsg8uUsT1B2F9eshigZHBRpuaD0D3mY8Qm2BfB5N2YyRzdNEYVDy0Ja-WsFjcOUuP1HvFLWA6H3XuHTUSmmDV2--0TXonxsKbp7G9C6R__NONS-MFNvxj_d6mBAgAA).
 
-Conversely, if `a` is `false`, `b` will not be evaluated, and the effect will _only_ re-run when `a` changes.
+Conversely, if `condition` is `false`, `color` will not be evaluated, and the effect will _only_ re-run again when `condition` changes.
 
 ```ts
-let a = false;
-let b = false;
+// @filename: ambient.d.ts
+declare module 'canvas-confetti' {
+	interface ConfettiOptions {
+		colors: string[];
+	}
+
+	function confetti(opts?: ConfettiOptions): void;
+	export default confetti;
+}
+
+// @filename: index.js
 // ---cut---
-$effect(() => {
-	console.log('running');
+import confetti from 'canvas-confetti';
+
+let condition = $state(true);
+let color = $state('#ff3e00');
 
-	if (a) {
-		console.log('b:', b);
+$effect(() => {
+	if (condition) {
+		confetti({ colors: [color] });
+	} else {
+		confetti();
 	}
 });
 ```
@@ -211,20 +225,19 @@ It is used to implement abstractions like [`createSubscriber`](/docs/svelte/svel
 
 The `$effect.root` rune is an advanced feature that creates a non-tracked scope that doesn't auto-cleanup. This is useful for nested effects that you want to manually control. This rune also allows for the creation of effects outside of the component initialisation phase.
 
-```svelte
-<script>
-	let count = $state(0);
-
-	const cleanup = $effect.root(() => {
+```js
+const destroy = $effect.root(() => {
 	$effect(() => {
-			console.log(count);
+		// setup
 	});
 
 	return () => {
-			console.log('effect root cleanup');
+		// cleanup
 	};
 });
-</script>
+
+// later...
+destroy();
 ```
 
 ## When not to use `$effect`