feat: add nutrition/food logging to fitness section

Daily food log with calorie and macro tracking against configurable diet
goals (presets: WHO balanced, cut, bulk, keto, etc.). Includes USDA/BLS
food search with portion-based units, favorite ingredients, custom
reusable meals, per-food micronutrient detail pages, and recipe-to-log
integration via AddToFoodLogButton. Extends FitnessGoal with nutrition
targets and adds birth year to user profile for BMR calculation.

src/routes/fitness/[stats=fitnessStats]/+page.svelte

@@ -40,7 +40,7 @@
 	let goalInput = $state(4);
 	let goalSaving = $state(false);
 
-	const hasDemographics = $derived(data.goal?.sex != null && data.goal?.heightCm != null);
+	const hasDemographics = $derived(data.goal?.sex != null && data.goal?.heightCm != null && data.goal?.birthYear != null);
 
 	function startGoalEdit() {
 		goalInput = goalWeekly ?? 4;