Add lessons module, rate cycles, EC2 deploy scripts, and help content

- Lessons module: lesson types, instructors, schedule slots, enrollments,
  sessions (list + week grid view), lesson plans, grading scales, templates
- Rate cycles: replace monthly_rate with billing_interval + billing_unit on
  enrollments; add weekly/monthly/quarterly rate presets to lesson types and
  schedule slots with auto-fill on enrollment form
- Member detail page: tabbed layout for details, identity documents, enrollments
- Sessions week view: custom 7-column grid replacing react-big-calendar
- Music store seed: instructors, lesson types, slots, enrollments, sessions,
  grading scale, lesson plan template
- Scrollbar styling: themed to match sidebar/app palette
- deploy/: EC2 setup and redeploy scripts, nginx config, systemd service
- Help: add Lessons category (overview, types, instructors, slots, enrollments,
  sessions, plans/grading); collapsible sidebar with independent scroll;
  remove POS/accounting references from docs

packages/admin/src/routes/_authenticated/accounts/$accountId.tsx

@@ -12,6 +12,7 @@ export const Route = createFileRoute('/_authenticated/accounts/$accountId')({
 const tabs = [
   { label: 'Overview', to: '/accounts/$accountId' },
   { label: 'Members', to: '/accounts/$accountId/members' },
+  { label: 'Enrollments', to: '/accounts/$accountId/enrollments' },
   { label: 'Payment Methods', to: '/accounts/$accountId/payment-methods' },
   { label: 'Tax Exemptions', to: '/accounts/$accountId/tax-exemptions' },
   { label: 'Processor Links', to: '/accounts/$accountId/processor-links' },