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/lib/services/entity-activity.service.ts

@@ -0,0 +1,42 @@
+import { inArray } from 'drizzle-orm';
+
+import { db } from '@/lib/db';
+import { user } from '@/lib/db/schema/users';
+import { searchAuditLogs } from '@/lib/services/audit-search.service';
+
+/**
+ * Shared loader for the per-entity Activity tab. Wraps `searchAuditLogs`
+ * with actor-email resolution so each row can render `who did what`.
+ *
+ * Tenant gate happens at the API route — this service trusts the caller
+ * to pass an entityId that belongs to `portId`.
+ */
+export async function loadEntityActivity(args: {
+  portId: string;
+  entityType: string;
+  entityId: string;
+  limit?: number;
+}) {
+  const { rows } = await searchAuditLogs({
+    portId: args.portId,
+    entityType: args.entityType,
+    entityId: args.entityId,
+    limit: args.limit ?? 50,
+  });
+
+  const userIds = Array.from(
+    new Set(rows.map((r) => r.userId).filter((u): u is string => Boolean(u))),
+  );
+  const userRows = userIds.length
+    ? await db
+        .select({ id: user.id, email: user.email, name: user.name })
+        .from(user)
+        .where(inArray(user.id, userIds))
+    : [];
+  const userMap = new Map(userRows.map((u) => [u.id, u]));
+
+  return rows.map((r) => ({
+    ...r,
+    actor: r.userId ? (userMap.get(r.userId) ?? null) : null,
+  }));
+}