fix(planner): rename gradient-protein-veg → gradient-protein-vegetarisch

The CSS variable key must match the actual tag name after umlaut
transliteration. 'veg' would never match a real tag named 'vegetarisch'.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/design-system/tokens.test.ts

@@ -57,7 +57,7 @@ const requiredTokens = [
 	'--gradient-protein-rind',
 	'--gradient-protein-fisch',
 	'--gradient-protein-tofu',
-	'--gradient-protein-veg',
+	'--gradient-protein-vegetarisch',
 	'--gradient-protein-schwein',
 	'--gradient-protein-lamm',
 	'--gradient-protein-ei',