Real BMR from weight change history, not just formula

Added BMR.estimateRealBmr(weights, foodTotals):
- Uses actual weight delta + total food intake over 30 days
- Formula: realExpenditure = (totalIntake + dWeight_kg * 7700) / days
- 7700 kcal per kg of fat, negative dWeight = weight loss
- Requires 3+ days of data and 2+ weight entries
- Sanity check: rejects < 500 kcal/day as bad data
- Overrides formula BMR when enough data available

renderToday now queries recent weights + food and uses real BMR
if calculated, falling back to Mifflin-St Jeor formula.

frontend/js/bmr.js

@@ -11,4 +11,20 @@ function getAge(birthYear) {
   return new Date().getFullYear() - birthYear;
 }
 
-window.BMR = { calculateBmr, getAge };
+// Estimate real daily expenditure from weight change + food intake.
+// weights: [{date, weight_kg}], foodTotals: [{date, kcal}]
+// Returns kcal/day or null if insufficient data.
+// Formula: realExpenditure = (totalIntake + weightDelta_kg * 7700) / days
+function estimateRealBmr(weights, foodTotals) {
+  if (!weights || weights.length < 2 || !foodTotals || foodTotals.length < 3) return null;
+  const firstW = weights[0];
+  const lastW = weights[weights.length - 1];
+  const days = Math.round((new Date(lastW.date) - new Date(firstW.date)) / 86400000);
+  if (days < 3) return null;
+  const dW = parseFloat(lastW.weight_kg) - parseFloat(firstW.weight_kg); // negative = lost weight
+  const totalIntake = foodTotals.reduce((s, d) => s + (d.kcal ?? 0), 0);
+  const realExpend = (totalIntake + dW * 7700) / days;
+  return realExpend > 500 ? Math.round(realExpend) : null; // sanity: < 500 kcal/day is wrong data
+}
+
+window.BMR = { calculateBmr, getAge, estimateRealBmr };

frontend/js/main.js

@@ -216,7 +216,14 @@ async function renderToday(container) {
     return;
   }
 
-  const bmr = calcBmr(weights);
+  let bmr = calcBmr(weights);
+  // Try to estimate real BMR from actual weight changes + food data (14 day window)
+  try {
+    const recentWeights = await DB.getRecentWeights(30);
+    const recentFood = await DB.getDailyFoodTotals(30);
+    const realBmr = BMR.estimateRealBmr(recentWeights, recentFood);
+    if (realBmr) bmr = realBmr;
+  } catch {}
   const intake  = Math.round(foodTotals.kcal ?? 0);
   const actKcal = Math.round(actTotals.kcal ?? 0);
   // Show expenditure even without BMR if there are activities