Track food eaten by weight in grams

Logging a meal now opens the dialog (like weigh-ins) with an optional
Amount (g) field; existing meals can get an amount via the edit dialog,
where clearing the field drops it. The overview's Meals tile shows the
day's total grams, and the weekly card gains a Food (grams) chart with
a self-scaling axis that stays hidden until any meal has an amount.

Events carry a new grams field (REAL column, auto-migrated); addEvent's
growing optional parameters are folded into an options object.

src/style.css

@@ -232,6 +232,12 @@ button.danger { background: var(--danger); }
   letter-spacing: 0.05em;
 }
 
+.stat-sub {
+  color: var(--muted);
+  font-size: 0.7rem;
+  margin-top: 2px;
+}
+
 .stat-value {
   font-size: 1.25rem;
   font-weight: 700;