Fix expenditure showing -- when BMR or profile incomplete

Two issues:
1. expend was null when BMR=null, even if GPS sessions had kcal.
   Now shows activity kcal alone if BMR unavailable.
2. calcBmr returned null if height/birth_year missing, but user
   had weight in profile. Now falls back: weight_log -> latestWeight
   -> profile.weight_kg. Also returns bmr_formula if height missing
   instead of null.

BMR calculation chain:
- bmr_estimated (manual override) takes priority
- Then formula: needs height + birth_year + weight (from any source)
- Then bmr_formula (pre-computed value in profile)
- Last resort: null → expenditure shows activity kcal only

frontend/js/main.js

@@ -219,7 +219,8 @@ async function renderToday(container) {
   const bmr = calcBmr(weights);
   const intake  = Math.round(foodTotals.kcal ?? 0);
   const actKcal = Math.round(actTotals.kcal ?? 0);
-  const expend  = bmr != null ? bmr + actKcal : null;
+  // Show expenditure even without BMR if there are activities
+  const expend  = bmr != null ? bmr + actKcal : actKcal > 0 ? actKcal : null;
   const balance = expend != null ? intake - expend : null;
   const hasGuessed = food.some(f => f.nutrients_guessed);
 
@@ -3902,13 +3903,19 @@ function createProductSearch(parentEl, onSelect, opts) {
 
 function calcBmr(weights) {
   const p = state.profile;
-  if (!p.height_cm || !p.birth_year) return null;
   if (p.bmr_estimated) return parseInt(p.bmr_estimated);
-  const kg = weights.length ? weights[weights.length - 1].weight_kg
-           : state.latestWeight?.weight_kg;
+  // Need height + birth_year for formula
+  const height = parseInt(p.height_cm);
+  const birthYear = parseInt(p.birth_year);
+  if (!height || !birthYear) return parseInt(p.bmr_formula) || null;
+  // Weight: today's weighing → latest weighing → profile weight
+  const kg = parseFloat(
+    (weights.length ? weights[weights.length - 1].weight_kg : null)
+    ?? state.latestWeight?.weight_kg
+    ?? p.weight_kg
+  );
   if (!kg) return parseInt(p.bmr_formula) || null;
-  return BMR.calculateBmr(kg, parseInt(p.height_cm),
-                          BMR.getAge(parseInt(p.birth_year)), p.sex ?? "m");
+  return BMR.calculateBmr(kg, height, BMR.getAge(birthYear), p.sex ?? "m");
 }
 
 function balanceClass(balance) {