Initial plugin scaffold: lesson scheduling WordPress plugin

- Custom DB tables for availability slots and lesson bookings
- Instructor (wp-admin) and student (front-end) roles with custom capabilities
- REST API under us-scheduler/v1 for availability CRUD and booking
- [us_booking] and [us_student_login] shortcodes for student front end
- PHPUnit + Brain\Monkey unit test suite (29 tests)
- Gitea Actions CI: lint, PHPStan, tests on PHP 8.1/8.2/8.3, no-debug check
- Feature docs under docs/features/

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

docs/features/availability-management.md

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+# Feature: Availability Management
+
+## Overview
+Instructors define date/time windows during which they are available for lessons. Students book from these windows.
+
+## Data Model — `{prefix}us_availability`
+
+| Column         | Type             | Notes                                        |
+|----------------|------------------|----------------------------------------------|
+| `id`           | BIGINT UNSIGNED  | Primary key                                  |
+| `instructor_id`| BIGINT UNSIGNED  | WordPress user ID                            |
+| `start_dt`     | DATETIME         | Slot start — stored as `Y-m-d H:i:s`        |
+| `end_dt`       | DATETIME         | Slot end — stored as `Y-m-d H:i:s`          |
+| `is_booked`    | TINYINT(1)       | 0 = available, 1 = booked                    |
+| `created_at`   | DATETIME         | Insertion time                               |
+
+## Admin Interface
+Instructors access **My Availability** in wp-admin (`?page=us-availability`).
+- Add a slot: provide start and end datetime
+- Delete a slot: only allowed if `is_booked = 0`
+
+## REST API
+| Method   | Endpoint                          | Permission              |
+|----------|-----------------------------------|-------------------------|
+| `GET`    | `/wp-json/us-scheduler/v1/availability`       | `book_lesson`           |
+| `POST`   | `/wp-json/us-scheduler/v1/availability`       | `manage_availability`   |
+| `DELETE` | `/wp-json/us-scheduler/v1/availability/{id}`  | `manage_availability` + slot owner |
+
+`GET` supports query params: `instructor_id`, `from` (datetime), `to` (datetime).
+
+## Implementation
+- Repository: `Unsupervised\Schedular\Data\AvailabilityRepository`
+- Model: `Unsupervised\Schedular\Model\AvailabilitySlot`
+- Admin controller: `Unsupervised\Schedular\Admin\AvailabilityController`
+- REST endpoint: `Unsupervised\Schedular\Api\AvailabilityEndpoint`
+
+## Tests
+- `tests/Unit/Data/AvailabilityRepositoryTest.php`
+- `tests/Unit/Model/AvailabilitySlotTest.php`