feat: UX enhancements, member limits, forecast fix, and menu cleanup (v2026.3.19)

- Onboarding wizard: add Reserve Account step between Operating and Assessments,
  redirect to Budget Planning on completion
- Dashboard: health score pending state shows clickable links to set up missing items
- Projects/Vendors: rich empty-state wizard screens with real-world examples and CTAs
- Investment Planning: auto-refresh AI recommendations when empty or stale (>30 days)
- Hide Invoices and Payments menus (see PARKING-LOT.md for re-enablement)
- Send welcome email via Resend when new members are added to a tenant
- Enforce 5-member limit for Starter/Standard/Professional plans (Enterprise unlimited)
- Cash flow forecast: only mark months as "Actual" when journal entries exist,
  fixing the issue where months without data showed as actuals
- Bump version to 2026.3.19

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

frontend/src/components/layout/Sidebar.tsx

@@ -73,8 +73,9 @@ const navSections = [
     label: 'Transactions',
     items: [
       { label: 'Transactions', icon: IconReceipt, path: '/transactions', tourId: 'nav-transactions' },
-      { label: 'Invoices', icon: IconFileInvoice, path: '/invoices' },
-      { label: 'Payments', icon: IconCash, path: '/payments' },
+      // Invoices and Payments hidden — see PARKING-LOT.md for future re-enablement
+      // { label: 'Invoices', icon: IconFileInvoice, path: '/invoices' },
+      // { label: 'Payments', icon: IconCash, path: '/payments' },
     ],
   },
   {