feat(domain): add core entities — Club, Member, WorkItem, Shift with state machine

- Create domain entities in WorkClub.Domain/Entities: Club, Member, WorkItem, Shift, ShiftSignup
- Implement enums: SportType, ClubRole, WorkItemStatus
- Add ITenantEntity interface for multi-tenancy support
- Implement state machine validation on WorkItem with C# 14 switch expressions
- Valid transitions: Open→Assigned→InProgress→Review→Done, Review→InProgress (rework)
- All invalid transitions throw InvalidOperationException
- TDD approach: Write tests first, 12/12 passing
- Use required properties with explicit Guid/Guid? for foreign keys
- DateTimeOffset for timestamps (timezone-aware, multi-tenant friendly)
- RowVersion byte[] for optimistic concurrency control
- No navigation properties yet (deferred to EF Core task)
- No domain events or validation attributes (YAGNI for MVP)

.sisyphus/evidence/task-5-dev-server.txt

@@ -0,0 +1,28 @@
+=== DEV SERVER VERIFICATION ===
+Date: 2026-03-03
+Task: Initialize Next.js 15 project - Dev server test
+
+DEV SERVER COMMAND: bun run dev
+STARTUP STATUS: SUCCESS
+PORT: 3000
+
+=== DEV SERVER OUTPUT ===
+$ next dev
+▲ Next.js 16.1.6 (Turbopack)
+- Local:         http://localhost:3000
+- Network:       http://192.168.241.158:3000
+
+✓ Starting...
+✓ Ready in 625ms
+ GET / 200 in 1187ms (compile: 1096ms, render: 91ms)
+
+=== HTTP RESPONSE TEST ===
+ENDPOINT: http://localhost:3000/
+HTTP STATUS CODE: 200
+RESPONSE: Success (HTML content returned)
+
+DEV SERVER VERIFICATION: PASSED
+- Server starts successfully ✓
+- Responds on port 3000 ✓
+- HTTP 200 response ✓
+- Request processing: 1187ms (acceptable for dev) ✓