fix: remove trailing semicolon from {@const} tag printer (#17962)

Fixes #17720 

## Problem
The `{@const}` tag was being printed with a trailing semicolon,
producing invalid Svelte syntax like:
{@const a = 1;}
This happened because the `ConstTag` visitor in the printer was
delegating to esrap's `VariableDeclaration` handler, which always
appends a semicolon (correct for JS, but wrong for Svelte template
syntax).

## Solution
Instead of delegating to `VariableDeclaration`, the `ConstTag` visitor
now manually prints the tag by:
- Writing `{@const ` directly
- Iterating through declarators and visiting each one
- Separating multiple declarations with commas
- Closing with `}` — no trailing semicolon

## Before
{@const a = 1;}
{@const a = 1, b = 2;}

## After
{@const a = 1}
{@const a = 1, b = 2}

## Changes
- `packages/svelte/src/compiler/print/index.js` — fixed `ConstTag`
visitor
- `packages/svelte/tests/print/samples/const-tag/output.svelte` —
updated expected test output

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Rich Harris <hello@rich-harris.dev>
Co-authored-by: Rich Harris <rich.harris@vercel.com>

.changeset/two-onions-end.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: remove trailing semicolon from {@const} tag printer

packages/svelte/src/compiler/print/index.js

@@ -592,8 +592,13 @@ const svelte_visitors = (comments) => ({
 	},
 
 	ConstTag(node, context) {
-		context.write('{@');
-		context.visit(node.declaration);
+		context.write('{@const ');
+		const declarators = node.declaration.declarations;
+		for (let i = 0; i < declarators.length; i++) {
+			if (i > 0) context.write(', ');
+			context.visit(declarators[i]);
+		}
+
 		context.write('}');
 	},
 

packages/svelte/tests/print/samples/const-tag/output.svelte

@@ -3,6 +3,6 @@
 </script>
 
 {#each boxes as box}
-	{@const area = box.width * box.height;}
+	{@const area = box.width * box.height}
 	{box.width} * {box.height} = {area}
 {/each}