feat(activity): per-entity Activity timeline (clients/yachts/companies/berths)

Until now only the global /admin/audit page surfaced audit_logs. Each
entity detail page either lacked the Activity tab entirely or rendered
"Activity log coming soon" text.

- entity-activity.service.loadEntityActivity wraps searchAuditLogs
  with actor-email resolution; reused by all 5 endpoints.
- New endpoints: /api/v1/{clients,yachts,companies,berths,interests}/[id]/activity,
  each gated on the per-entity .view permission and tenant-checked
  against ctx.portId.
- EntityActivityFeed renders a timeline with action verb ("Updated",
  "Archived"), actor name, relative time, and field old→new diff.
- client-tabs, yacht-tabs, company-tabs, berth-tabs now mount the feed
  on their Activity tab. Interest already has the richer
  InterestTimeline component.
- yacht-tabs YachtInterestsTab also gets a friendlier empty state with
  guidance copy.

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

src/components/yachts/yacht-tabs.tsx

@@ -7,6 +7,7 @@ import type { DetailTab } from '@/components/shared/detail-layout';
 import { InlineEditableField } from '@/components/shared/inline-editable-field';
 import { InlineTagEditor } from '@/components/shared/inline-tag-editor';
 import { NotesList } from '@/components/shared/notes-list';
+import { EntityActivityFeed } from '@/components/shared/entity-activity-feed';
 import { ReservationList, type ReservationRow } from '@/components/reservations/reservation-list';
 import { YachtOwnershipHistory } from '@/components/yachts/yacht-ownership-history';
 import { apiFetch } from '@/lib/api/client';
@@ -225,7 +226,15 @@ function YachtInterestsTab({ yachtId }: { yachtId: string }) {
 
   if (isLoading) return <p className="text-sm text-muted-foreground">Loading…</p>;
   if (interests.length === 0) {
-    return <p className="text-sm text-muted-foreground">No interests linked to this yacht.</p>;
+    return (
+      <div className="rounded-md border border-dashed bg-muted/30 p-6 text-center">
+        <p className="text-sm font-medium">No interests linked to this yacht</p>
+        <p className="text-xs text-muted-foreground mt-1">
+          Interests for this yacht will appear here once a sales rep links them. Add an interest
+          from the Interests tab on the owner&rsquo;s client page.
+        </p>
+      </div>
+    );
   }
 
   return (
@@ -298,5 +307,15 @@ export function getYachtTabs({ yachtId, currentUserId, yacht }: YachtTabsOptions
       label: 'Notes',
       content: <NotesList entityType="yachts" entityId={yachtId} currentUserId={currentUserId} />,
     },
+    {
+      id: 'activity',
+      label: 'Activity',
+      content: (
+        <EntityActivityFeed
+          endpoint={`/api/v1/yachts/${yachtId}/activity`}
+          emptyText="No activity recorded for this yacht yet."
+        />
+      ),
+    },
   ];
 }