Add category.move to reparent a category.

Validates both source and target via resolveCategoryAccess so the new
parent must be a category of the same authorized company, and guards
against moving into a descendant (cycle). Assigns next sibling sort.

src/sql/category.js

@@ -103,6 +103,30 @@ SET sort = @sort
 WHERE id = @id AND parent_id = @parentId
 `;
 
+/** True if @id is an ancestor of @parentId (would create a cycle when moving). */
+export const IS_ANCESTOR = `
+WITH ancestors AS (
+    SELECT id, parent_id
+    FROM category
+    WHERE id = @parentId
+
+    UNION ALL
+
+    SELECT c.id, c.parent_id
+    FROM category c
+    INNER JOIN ancestors a ON c.id = a.parent_id
+)
+SELECT id
+FROM ancestors
+WHERE id = @id
+`;
+
+export const MOVE = `
+UPDATE category
+SET parent_id = @parentId, sort = @sort
+WHERE id = @id
+`;
+
 export const DELETE = `
 DELETE FROM category
 WHERE id = @id