refactor: move scaler out of $lib/server so it can run in browser

RecipeView needs scaleIngredients on the client for live portion scaling.
Moved scaler.ts from $lib/server/recipes/ to $lib/recipes/.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/unit/scaler.test.ts

@@ -1,5 +1,5 @@
 import { describe, it, expect } from 'vitest';
-import { scaleIngredients, roundQuantity } from '../../src/lib/server/recipes/scaler';
+import { scaleIngredients, roundQuantity } from '../../src/lib/recipes/scaler';
 import type { Ingredient } from '../../src/lib/types';
 
 const mk = (q: number | null, unit: string | null, name: string): Ingredient => ({