[CLAUDE] Phase5.1: Security headers + account lockout + Users management

Security hardening:
- Api/Middleware/SecurityHeadersMiddleware MOI: remove server fingerprint (Server, X-Powered-By, ...), add X-Content-Type-Options:nosniff, X-Frame-Options:DENY, Referrer-Policy:strict-origin-when-cross-origin, Permissions-Policy (disable geolocation/mic/cam/payment), X-Permitted-Cross-Domain-Policies:none, CSP (default-src 'self' + img data: + style inline for Tailwind + frame-ancestors 'none'). Skip CSP tren /swagger (dung inline script).
- Program.cs wire UseMiddleware SecurityHeadersMiddleware first in pipeline
- Infrastructure/DependencyInjection Identity options:
  - Password.RequiredLength config-driven (Identity:Password:RequiredLength, default 8 dev, override 12+ prod)
  - Lockout: DefaultLockoutTimeSpan (15min), MaxFailedAccessAttempts (5), AllowedForNewUsers=true — all config-driven
- LoginCommandHandler: IsLockedOutAsync check truoc → throw voi deadline message, AccessFailedAsync khi sai password, ResetAccessFailedCountAsync khi login thanh cong

Users management:
- Application/Users/UserFeatures.cs: 8 CQRS (ListUsersQuery paging+search, GetUserQuery, CreateUserCommand + Validator, UpdateUserCommand voi self-disable protection, AssignRolesCommand voi self-demote protection (khong tu go Admin), ResetPasswordCommand (invalidate refresh token + unlock), UnlockUserCommand)
- UserDto: Id, Email, FullName, IsActive, IsLocked (computed tu LockoutEnd), CreatedAt, Roles
- Api/Controllers/UsersController: 7 endpoint (Users.Read/Create/Update policies):
  - GET / (list paged), GET /{id}, POST /, PUT /{id}, PUT /{id}/roles, POST /{id}/reset-password, POST /{id}/unlock
- using alias ValidationException = Application.Common.Exceptions.ValidationException (fix ambiguity voi FluentValidation)

Frontend fe-admin:
- types/users.ts MOI: User type + AVAILABLE_ROLES 12 role (match BE AppRoles.cs) + RoleLabel Vietnamese
- pages/system/UsersPage.tsx MOI:
  - DataTable columns: Email (mono), FullName, Roles (badge chips voi Vietnamese label), IsActive (CheckCircle/XCircle), IsLocked (KeyRound red), CreatedAt
  - Actions per row (PermissionGuard Users.Update wrap): Gan role (Shield icon → Dialog grid 12 checkbox), Reset password (KeyRound → Dialog voi warning user se bi logout), Unlock (Unlock icon, chi hien khi isLocked), Toggle active (XCircle/CheckCircle)
  - Create user dialog: email + fullName + password (min 8) + grid 12 role checkbox
- Route /system/users vao App.tsx

E2E verified:
- Security headers present tren moi response (check qua curl -I)
- POST /api/users voi roles: [Drafter] → 201 + id
- GET /api/users → paged voi 2 user (admin + new test.drafter)
- TS check fe-admin → pass
- dotnet build → 0 errors

Docs:
- docs/STATUS.md: Phase 5.1 xong, cumulative BE 3700 LOC, 42 endpoints, 17 FE pages
- docs/HANDOFF.md: phase table update row Phase 5.1, last updated timestamp
- docs/changelog/migration-todos.md: tick 6 items Phase 5.1 + 4 items remaining (IDOR, deps scan, admin warning, Roles CRUD)
- docs/changelog/sessions/2026-04-21-1630-phase5-1-security-users.md: session log

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
EOF

src/Backend/SolutionErp.Api/Middleware/SecurityHeadersMiddleware.cs

@@ -0,0 +1,42 @@
+namespace SolutionErp.Api.Middleware;
+
+// Thêm security headers theo OWASP + Mozilla Observatory best practices.
+// Xem docs/guides/security-checklist.md §A05.
+public class SecurityHeadersMiddleware(RequestDelegate next)
+{
+    public async Task InvokeAsync(HttpContext context)
+    {
+        var headers = context.Response.Headers;
+
+        // Ẩn server fingerprint
+        headers.Remove("Server");
+        headers.Remove("X-Powered-By");
+        headers.Remove("X-AspNet-Version");
+        headers.Remove("X-AspNetMvc-Version");
+
+        // Security headers
+        headers["X-Content-Type-Options"] = "nosniff";
+        headers["X-Frame-Options"] = "DENY";
+        headers["Referrer-Policy"] = "strict-origin-when-cross-origin";
+        headers["X-Permitted-Cross-Domain-Policies"] = "none";
+        headers["Permissions-Policy"] = "geolocation=(), microphone=(), camera=(), payment=()";
+
+        // CSP chỉ áp dụng ở non-Swagger (Swagger dùng inline script/style)
+        var isSwagger = context.Request.Path.StartsWithSegments("/swagger");
+        if (!isSwagger)
+        {
+            headers["Content-Security-Policy"] =
+                "default-src 'self'; " +
+                "img-src 'self' data:; " +
+                "style-src 'self' 'unsafe-inline'; " +  // Tailwind cần inline styles ở runtime
+                "script-src 'self'; " +
+                "font-src 'self' data:; " +
+                "connect-src 'self'; " +
+                "frame-ancestors 'none'; " +
+                "base-uri 'self'; " +
+                "form-action 'self'";
+        }
+
+        await next(context);
+    }
+}