fix(audit-tier-4): tenant-isolation defense-in-depth

Closes the audit's HIGH §10 + MED §§17–22 isolation footguns. None of
these are user-impactful TODAY — every site is preceded by a port-
scoped read or pre-validated by ctx.portId — but each is a future-
refactor accident waiting to happen, so the SQL itself now pins the
tenant boundary:

* mergeClients gains a callerPortId option; the route caller passes
  ctx.portId.  removeInterestBerth now requires portId and verifies
  both the interest and the berth share it before deleting the
  junction row.  All three callers updated.
* Six service mutations now scope the WHERE to (id, portId):
  form-templates update + delete, invoices.detectOverdue per-row
  update, notifications.markRead, clients.deleteRelationship.
  company-memberships uses an inArray sub-select against port
  companies (no port_id column on the table itself), covering
  updateMembership / endMembership / setPrimary.
* Port-scoped file lookups in portal.getDocumentDownloadUrl,
  reports.getDownloadUrl (file presign), berth-reservations.activate
  (contractFileId attach guard), and residential.getResidentialInterestById
  (residentialClient join).

Test status: 1168/1168 vitest, tsc clean.

Refs: docs/audit-comprehensive-2026-05-05.md HIGH §10 + MED §§17–22
(auditor-B3 Issues 1–5,7).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/lib/services/interests.service.ts

@@ -563,7 +563,7 @@ export async function updateInterest(
         addedBy: meta.userId,
       });
     } else if (currentBerthId) {
-      await removeInterestBerth(id, currentBerthId);
+      await removeInterestBerth(id, currentBerthId, portId);
     }
   }
 
@@ -981,7 +981,7 @@ export async function unlinkBerth(id: string, portId: string, meta: AuditMeta) {
   const oldBerthId = previousPrimary?.berthId ?? null;
 
   if (oldBerthId) {
-    await removeInterestBerth(id, oldBerthId);
+    await removeInterestBerth(id, oldBerthId, portId);
   }
 
   const [updated] = await db