feat(splits): save split as rule from split modal

- Checkbox in split modal: 'Also save as rule for <merchant>'
- Creates a rule with apply_split action storing the participant shares
- Rules engine now handles apply_split: deletes existing splits and re-applies
- Bulk split mode hides the checkbox (rule wouldn't make sense for ad-hoc bulk)

src/app/api/rules/apply/route.ts

@@ -9,10 +9,16 @@ interface Condition {
   value: string;
 }
 
+interface SplitEntry {
+  participant_id: number;
+  share_percent: number;
+}
+
 interface Actions {
   set_category?: string;
   add_tag_ids?: number[];
   set_merchant?: string;
+  apply_split?: SplitEntry[];
 }
 
 interface TxFields {
@@ -108,6 +114,18 @@ export async function POST(req: NextRequest) {
           );
         }
       }
+
+      if (actions.apply_split?.length) {
+        // Delete existing splits then insert new ones
+        await queryRaw(`DELETE FROM transaction_splits WHERE transaction_id = $1`, [tx.id]);
+        for (const s of actions.apply_split) {
+          await queryRaw(
+            `INSERT INTO transaction_splits (transaction_id, participant_id, share_percent)
+             VALUES ($1, $2, $3) ON CONFLICT DO NOTHING`,
+            [tx.id, s.participant_id, s.share_percent]
+          );
+        }
+      }
     }
   }