feat: register export sector with 4 extension definitions

Add export & utrikeshandel sector to the extension system with BAS
accounts (3105, 3108, 3109, 3521, 3522), sector metadata, icon
imports, workspace registry entries, and design document.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/extensions/icon-resolver.tsx

@@ -23,6 +23,9 @@ import {
   BarChart3,
   Layers,
   Puzzle,
+  Ship,
+  FileText,
+  Shield,
   type LucideIcon,
 } from 'lucide-react'
 
@@ -51,6 +54,9 @@ const ICON_MAP: Record<string, LucideIcon> = {
   BarChart3,
   Layers,
   Puzzle,
+  Ship,
+  FileText,
+  Shield,
 }
 
 export function resolveIcon(name: string): LucideIcon {