fix: hide unlinked old activities from current work

Imported follow-ups with no person, company, or deal stayed on the board because only linked prior records were archived.

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/api/src/billing/billing.service.ts

@@ -305,6 +305,13 @@ export class BillingService {
                 SELECT 1 FROM "Deal" AS d2
                 WHERE d2."id" = a."dealId" AND d2."importSource" = 'didar'
               )
+              OR (
+                a."personId" IS NULL
+                AND a."companyId" IS NULL
+                AND a."dealId" IS NULL
+                AND a."dueAt" IS NOT NULL
+                AND a."dueAt" < ${cutoff}
+              )
             )
           )
         )