feat: support unassigned purchases and allocation status

Allow month-only purchases to start finance plans. Keep unbudgeted posts distinct from explicit zero rules in overspend reporting.

src/ui/components/PurchaseDialog.tsx

@@ -49,6 +49,7 @@ export function PurchaseDialog({ monthId, purchase, trigger }: Props) {
     .sort((a, b) => a.order - b.order);
 
   const [open, setOpen] = useState(false);
+  const [detachBill, setDetachBill] = useState(false);
   const [draft, setDraft] = useState<PurchaseDraft>(() =>
     purchase ? fromPurchase(purchase) : emptyDraft(monthId, activePosts[0]?.id ?? ""),
   );
@@ -68,6 +69,7 @@ export function PurchaseDialog({ monthId, purchase, trigger }: Props) {
   const errors = bulkMode ? validateBulk(bulk) : validatePurchase(draft);
 
   function reset() {
+    setDetachBill(false);
     setDraft(
       purchase ? fromPurchase(purchase) : emptyDraft(monthId, activePosts[0]?.id ?? ""),
     );
@@ -86,7 +88,10 @@ export function PurchaseDialog({ monthId, purchase, trigger }: Props) {
     const created = bulkMode ? toPurchases(bulk) : null;
     void mutate((data) => {
       if (created) for (const p of created) addPurchase(data, p);
-      else if (purchase) updatePurchase(data, purchase.id, toPurchase(draft));
+      else if (purchase) updatePurchase(data, purchase.id, {
+        ...toPurchase(draft),
+        ...(detachBill ? { source: undefined } : {}),
+      });
       else addPurchase(data, toPurchase(draft));
     }).then((saved) => {
       if (!saved) return;
@@ -166,7 +171,7 @@ export function PurchaseDialog({ monthId, purchase, trigger }: Props) {
                       setBulk((b) => ({ ...b, postId }));
                     }}
                   >
-                    <option value="">Choose a post…</option>
+                    <option value="">No post (unassigned)</option>
                     {activePosts.map((post) => (
                       <option key={post.id} value={post.id}>
                         {post.name}
@@ -301,6 +306,17 @@ export function PurchaseDialog({ monthId, purchase, trigger }: Props) {
 
           <SplitEditor draft={draft} posts={activePosts} onChange={setDraft} />
 
+          {purchase?.source && (
+            <label className="flex items-start gap-2 text-sm">
+              <input
+                type="checkbox"
+                checked={detachBill}
+                onChange={(event) => setDetachBill(event.target.checked)}
+              />
+              <span>Unlink from bill. The occurrence will show as expected again.</span>
+            </label>
+          )}
+
           <PlanEditor draft={draft} onChange={setDraft} />
             </>
           )}