Add feature specs for booking platform requirements

Update availability, lesson-booking, and user-roles docs and add specs
for offerings, group classes, registration questions, versioned policies,
Stripe payments (with e-transfer/comp overrides and receipts), and
monthly per-instructor payment reporting. Tracked in issues #1-#9.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/features/payment-reporting.md

@@ -0,0 +1,49 @@
+# Feature: Payment Reporting
+
+## Overview
+A monthly view of payments per instructor, with a downloadable spreadsheet (CSV) export. The studio admin sees every instructor and can filter; each instructor sees only their own payments. The report is built entirely from `us_payments` — no additional table.
+
+## Data Source
+Reads `{prefix}us_payments` (see `payments.md`), grouped by calendar month and
+instructor. Each report row joins through to the student and offering for display:
+
+| Report Column | Source                                            |
+|---------------|---------------------------------------------------|
+| Date          | `us_payments.paid_at` (falls back to `created_at`) |
+| Student       | `us_payments.student_id` → display name           |
+| Offering      | registration → `us_offerings.title`               |
+| Method        | `us_payments.method`                              |
+| Status        | `us_payments.status`                              |
+| Amount        | `us_payments.amount_cents` / `currency`           |
+
+Totals are summed over `paid` rows for the selected month.
+
+## Access Rules
+- Studio admin (`view_all_payments`): all instructors; may filter by `instructor_id`.
+- Instructor (`view_own_payments`): rows where `us_payments.instructor_id` is their own user ID only.
+- Export requires `export_payments` and is scoped to the same rows the caller may view.
+
+## Admin Interface
+**Payments** in wp-admin:
+- Month picker (defaults to the current month) and, for studio admin, an instructor filter
+- A table of payments with a monthly total
+- An **Export** button that downloads the filtered rows as CSV
+
+## REST API
+| Method | Endpoint                                       | Permission           |
+|--------|------------------------------------------------|----------------------|
+| `GET`  | `/wp-json/us-scheduler/v1/payments`            | `view_own_payments` or `view_all_payments` |
+| `GET`  | `/wp-json/us-scheduler/v1/payments/export`     | `export_payments`    |
+
+Query params: `month` (`YYYY-MM`, required), `instructor_id` (optional; ignored for
+instructors, who are always scoped to themselves). `GET /payments/export` returns
+`text/csv` with a `Content-Disposition` attachment header.
+
+## Implementation
+- Report controller: `Unsupervised\Schedular\Payment\PaymentReportController`
+- CSV exporter: `Unsupervised\Schedular\Payment\PaymentExporter`
+- Report query: `Unsupervised\Schedular\Payment\PaymentRepository::report()`
+
+## Tests
+- `tests/Unit/Payment/PaymentReportControllerTest.php`
+- `tests/Unit/Payment/PaymentExporterTest.php`