Node: members

R1. POST /api/members body { "username": "...", "email": "..." } → 201 { "member": { "id": ..., "username": "...", "email": "...", "createdAt": "<ISO>" } }. R2. Validation: username required, non-empty; email must match a basic email regex. Violation → 422 { "errors": { "<field>": ["<msg>"] } }. R3. Duplicate username → 409 { "errors": { "username": ["already taken"] } }. R4. GET /api/members?limit=&offset= → 200 { "members": [...], "total": <int> }. Default limit=20, offset=0. total = FULL count (not the page size). R5. GET /api/members/:id → 200 { "member": {...} } or 404 { "errors": { "member": ["not found"] } }. R11. DELETE /api/members/:id → 204; a subsequent GET → 404; its activity is deleted too (cascade).