Роли ADMIN и USER, User panel и Admin panel

- Роль ADMIN = users.is_admin; встроенный администратор (mailserver.admins, по
  умолчанию admin@) всегда ADMIN и получает роль в базе при старте.
- PUT /api/admin/mailboxes/{id}/role {ADMIN|USER}: только ADMIN; не свою, не
  встроенного, общий ящик не может быть ADMIN.
- Admin panel (/admin, только ADMIN): USERS (логины и роли, MAKE ADMIN / MAKE USER),
  MAILBOXES, LISTS. User panel (/settings): профиль, пароль, хранилище, вид, мои ящики.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/src/main/java/com/mailserver/controller/MailboxAdminController.java

@@ -45,8 +45,13 @@ public class MailboxAdminController {
     private static final Logger log = LoggerFactory.getLogger(MailboxAdminController.class);
     private static final int MIN_PASSWORD = MailDirectory.MIN_PASSWORD;
 
+    /** @param role ADMIN or USER; @param builtIn the administrator from the configuration — the role stays */
     public record MailboxView(Long id, String email, String displayName, boolean active, boolean admin, boolean trap,
-                              boolean shared, List<String> members, long usedBytes, long quotaBytes, Instant createdAt) {
+                              boolean shared, List<String> members, long usedBytes, long quotaBytes, Instant createdAt,
+                              String role, boolean builtIn) {
+    }
+
+    public record RoleRequest(String role) {
     }
 
     /** @param password empty — the server generates one and returns it once */
@@ -171,6 +176,30 @@ public class MailboxAdminController {
         }));
     }
 
+    /** Role ADMIN (manages mailboxes, lists, roles — Admin panel) or USER. Not your own, not the built-in administrator. */
+    @PutMapping("/{id}/role")
+    public Mono<MailboxView> role(Mono<Authentication> auth, @PathVariable Long id, @RequestBody Mono<RoleRequest> body) {
+        return admin(auth).flatMap(me -> body.flatMap(request -> mailbox(id).flatMap(user -> {
+            if (!"ADMIN".equals(request.role()) && !"USER".equals(request.role())) {
+                return Mono.error(bad("Role: ADMIN or USER"));
+            }
+            boolean toAdmin = "ADMIN".equals(request.role());
+            if (user.getEmail().equalsIgnoreCase(me)) {
+                return Mono.error(bad("You can not change your own role"));
+            }
+            if (!toAdmin && admins.isBuiltIn(user.getEmail())) {
+                return Mono.error(bad("The built-in administrator stays ADMIN"));
+            }
+            if (toAdmin && user.isShared()) {
+                return Mono.error(bad("A shared mailbox has no login of its own — it can not be ADMIN"));
+            }
+            return users.setAdmin(user, toAdmin).doOnNext(u -> {
+                admins.grant(u.getEmail(), toAdmin);
+                log.warn("Mailbox {} role {} given by administrator {}", u.getEmail(), request.role(), me);
+            });
+        }))).flatMap(this::view);
+    }
+
     /** Trap: what the mailbox sends is stored in its own INBOX, nothing leaves the server (staging@). */
     @PutMapping("/{id}/trap")
     public Mono<MailboxView> trap(Mono<Authentication> auth, @PathVariable Long id, @RequestBody Mono<TrapRequest> body) {
@@ -237,7 +266,7 @@ public class MailboxAdminController {
         return mail.usedBytes(user.getId()).defaultIfEmpty(0L).zipWith(access.members(user.getId()).collectList())
                 .map(pair -> new MailboxView(user.getId(), user.getEmail(), user.getDisplayName(), user.isActive(),
                         admins.isAdmin(user.getEmail()), user.isTrap(), user.isShared(), pair.getT2(), pair.getT1(), user.getQuotaBytes() == null ? 0 : user.getQuotaBytes(),
-                        user.getCreatedAt()));
+                        user.getCreatedAt(), admins.isAdmin(user.getEmail()) ? "ADMIN" : "USER", admins.isBuiltIn(user.getEmail())));
     }
 
     private static ResponseStatusException bad(String message) {