fix(fitness): exclude 0-kcal days from calorie balance stats

Average calorie balance was comparing logged-day intake against all-day
expenditure, producing a spurious deficit on weeks with untracked days.
Now restrict both sides to days with non-zero logged intake so the
subtraction compares apples to apples.

package.json

@@ -1,6 +1,6 @@
 {
 	"name": "homepage",
-	"version": "1.37.4",
+	"version": "1.37.5",
 	"private": true,
 	"type": "module",
 	"scripts": {