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/app.css

@@ -89,6 +89,30 @@ body {
   transition: background-color 5000s ease-in-out 0s;
 }
 
+/* Scrollbars — themed to match sidebar/app palette */
+* {
+  scrollbar-width: thin;
+  scrollbar-color: var(--border) transparent;
+}
+
+*::-webkit-scrollbar {
+  width: 6px;
+  height: 6px;
+}
+
+*::-webkit-scrollbar-track {
+  background: transparent;
+}
+
+*::-webkit-scrollbar-thumb {
+  background-color: var(--border);
+  border-radius: 9999px;
+}
+
+*::-webkit-scrollbar-thumb:hover {
+  background-color: var(--muted-foreground);
+}
+
 /* Prevent browser autofill from overriding dark theme input colors */
 input:-webkit-autofill,
 input:-webkit-autofill:hover,