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/app/api/v1/admin/duplicates/handlers.ts

@@ -110,6 +110,7 @@ export async function confirmMergeHandler(
       winnerId: body.winnerId,
       loserId,
       mergedBy: ctx.userId,
+      callerPortId: ctx.portId,
       fieldChoices: body.fieldChoices,
     });
 

src/app/api/v1/interests/[id]/berths/[berthId]/handlers.ts

@@ -124,7 +124,7 @@ export const deleteHandler: RouteHandler = async (_req, ctx, params) => {
 
     await loadScopedRow(interestId, berthId, ctx.portId);
 
-    await removeInterestBerth(interestId, berthId);
+    await removeInterestBerth(interestId, berthId, ctx.portId);
 
     void createAuditLog({
       userId: ctx.userId,