Auto-derive total cannabinoids from THC + CBD when adding inventory

Total cannabinoids % now defaults to THC + CBD and stays in sync as
either field changes. Once the user manually edits the total field it
stops auto-updating, since some labels list an explicit total that
differs from the sum. When autofilling from a previous instance the
field is treated as manual (preserving the stored value).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/src/components/modals/AddInventoryFlow.tsx

@@ -375,7 +375,7 @@ function InstanceDetailsStep({
     price: initialPrice,
     thc: last?.thc ?? (cfg?.showCannabinoidPct !== false ? 22 : 0),
     cbd: last?.cbd ?? (cfg?.showCannabinoidPct !== false ? 0.4 : 0),
-    totalCannabinoids: last?.totalCannabinoids ?? (cfg?.showCannabinoidPct !== false ? 26 : 0),
+    totalCannabinoids: last?.totalCannabinoids ?? (cfg?.showCannabinoidPct !== false ? 22.4 : 0),
     purchaseDate: getToday(getStoredTimezone()),
   });
   const [newShopName, setNewShopName] = useState("");
@@ -383,10 +383,17 @@ function InstanceDetailsStep({
   const [newBinName, setNewBinName] = useState("");
   const [newBinCapacity, setNewBinCapacity] = useState(10);
   const [containerWeight, setContainerWeight] = useState("");
+  const [totalCannaManual, setTotalCannaManual] = useState(!!last);
   const [error, setError] = useState<string | null>(null);
 
   const update = <K extends keyof typeof form>(k: K, v: (typeof form)[K]) =>
-    setForm((f) => ({ ...f, [k]: v }));
+    setForm((f) => {
+      const next = { ...f, [k]: v };
+      if ((k === "thc" || k === "cbd") && !totalCannaManual) {
+        next.totalCannabinoids = +(next.thc + next.cbd).toFixed(1);
+      }
+      return next;
+    });
 
   const cpg = !isDiscrete && form.weight > 0 ? form.price / form.weight : 0;
   const assetIdValid = ASSET_ID_RE.test(assetId);
@@ -677,7 +684,10 @@ function InstanceDetailsStep({
                   type="number"
                   step="0.1"
                   value={form.totalCannabinoids}
-                  onChange={(e) => update("totalCannabinoids", +e.target.value)}
+                  onChange={(e) => {
+                    setTotalCannaManual(true);
+                    update("totalCannabinoids", +e.target.value);
+                  }}
                 />
               </Field>
             </div>