Restructure src/ and tests/ from package-by-type to package-by-domain

All classes are now organised by domain (Availability, Booking, Auth).
Each domain package contains its value object, repository, admin controller,
REST endpoint, and any shortcode pages under a matching sub-namespace.
Cross-cutting wiring (Plugin, AdminMenu, RestRegistrar, ShortcodeRegistrar,
Schema) lives at src/ root. Tests mirror the domain structure.

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

memory/feedback_architecture.md

@@ -0,0 +1,16 @@
+---
+name: Package-by-domain architecture
+description: New features must be organised as domain packages, not by type (no Admin/, Api/, Data/ etc.)
+type: feedback
+---
+
+Always organise code package-by-domain, not package-by-type.
+
+**Why:** User explicitly requested the restructure on 2026-03-30. Package-by-type (Admin/, Api/, Data/, Frontend/, Model/, Roles/) was the initial scaffold but was replaced before any real features shipped.
+
+**How to apply:**
+- New domain → new directory under `src/<Domain>/` (e.g. `src/Availability/`, `src/Booking/`, `src/Auth/`)
+- All classes for a domain (value objects, repositories, admin controllers, REST endpoints, shortcode pages) live inside that directory under the sub-namespace `Unsupervised\Schedular\<Domain>\`
+- Cross-cutting wiring that glues domains together (Plugin, AdminMenu, RestRegistrar, ShortcodeRegistrar, Schema) lives at `src/` root with namespace `Unsupervised\Schedular\`
+- Tests mirror the domain structure: `tests/Unit/<Domain>/`
+- Never create `src/Admin/`, `src/Api/`, `src/Data/`, `src/Frontend/`, `src/Model/`, or `src/Roles/` directories