Несколько ящиков у одного логина, общие ящики, кто ответил, вход ящик*логин

- V7: users.is_shared, mailbox_access (MEMBER от админа/Jambotron, ATTACHED по паролю ящика), messages.answered_by
- /api/mailboxes: мои ящики с непрочитанными, сессия другого ящика (JWT с claim by), подключить по паролю
  (LoginGuard), убрать из меню
- общий ящик: без своего входа (веб/SMTP/IMAP), участники открывают; «прочитано» общее; ответ из веба → answered_by
- SMTP/IMAP: ящик*логин + пароль логина (как master user в Dovecot)
- открытый чужой ящик (общий, подключённый, OPEN админа): профиль и пароль не меняются (403)
- админ: создать shared, участники ящика (PUT /{id}/members); служебное API: PUT /shared/{address};
  выключение аккаунта убирает и из общих ящиков
- UI: MAILBOXES в левом меню (переключение, ⊕ подключить, × убрать), shared/участники в настройках,
  «Answered by» у письма
- 88 тестов; живой прогон на Postgres 17 (апгрейд V6→V7 на данных), скриншоты UI

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

frontend/src/app/pages/shell/shell.component.ts

@@ -8,7 +8,7 @@ import { filter } from 'rxjs';
 import { ApiService } from '../../core/api.service';
 import { AuthService } from '../../core/auth.service';
 import { MailStateService } from '../../core/mail-state.service';
-import { Folder, errorText, folderIcon, folderLabel, formatBytes } from '../../core/models';
+import { Folder, MailboxEntry, errorText, folderIcon, folderLabel, formatBytes } from '../../core/models';
 import { BackgroundComponent } from '../../ui/background.component';
 import { DialogService } from '../../ui/dialog.service';
 import { THEMES, ThemeService } from '../../ui/theme.service';
@@ -81,6 +81,44 @@ import { ToastService } from '../../ui/toast.service';
       <div class="flex-grow max-w-[1500px] w-full mx-auto p-3 md:p-5 grid grid-cols-1 lg:grid-cols-[260px_1fr] gap-5">
         <nav class="glass-panel static p-4 md:pt-6 h-fit lg:sticky lg:top-20 lg:block" [class.hidden]="!menuOpen()"
              aria-label="Mail folders">
+          <div class="flex items-center justify-between mb-2 px-1">
+            <h2 class="text-[11px] font-orbitron font-bold text-cyan-300 tracking-widest">MAILBOXES</h2>
+            <button type="button" class="text-slate-400 hover:text-cyan-300" matTooltip="Add a mailbox you have the password of"
+                    aria-label="Add mailbox" [attr.aria-expanded]="attachOpen()" (click)="attachOpen.set(!attachOpen())">
+              <mat-icon class="!text-xl">add_circle_outline</mat-icon></button>
+          </div>
+          <ul class="space-y-1 mb-3" aria-label="Your mailboxes">
+            @for (b of boxes(); track b.email) {
+              <li class="flex items-center gap-1">
+                <button type="button" (click)="switchTo(b)" [attr.aria-current]="b.email === auth.email() ? 'true' : null"
+                        class="flex-grow flex items-center gap-2 px-3 py-1.5 rounded-lg border text-left font-rajdhani font-semibold min-w-0"
+                        [class.border-pink-500/40]="b.email === auth.email()" [class.bg-pink-500/15]="b.email === auth.email()"
+                        [class.text-pink-200]="b.email === auth.email()" [class.border-transparent]="b.email !== auth.email()"
+                        [class.text-slate-300]="b.email !== auth.email()"
+                        [matTooltip]="b.email + (b.shared ? ' — shared' : b.kind === 'ATTACHED' ? ' — attached' : '')">
+                  <mat-icon class="!text-lg shrink-0">{{ b.shared ? 'groups' : b.kind === 'OWN' ? 'person' : 'link' }}</mat-icon>
+                  <span class="flex-grow truncate text-sm">{{ b.email }}</span>
+                  @if (b.unread) {
+                    <span class="text-[11px] font-mono px-2 rounded-full bg-pink-500/25 text-pink-300" [attr.aria-label]="b.unread + ' unread'">{{ b.unread }}</span>
+                  }
+                </button>
+                @if (b.kind !== 'OWN') {
+                  <button type="button" class="text-slate-500 hover:text-pink-400" [attr.aria-label]="'Remove ' + b.email + ' from my mailboxes'"
+                          matTooltip="Remove from my mailboxes" (click)="leave(b)"><mat-icon class="!text-base">close</mat-icon></button>
+                }
+              </li>
+            }
+          </ul>
+          @if (attachOpen()) {
+            <form class="space-y-2 mb-4 p-2 rounded-lg border border-cyan-500/20" (ngSubmit)="attach()" aria-label="Add a mailbox">
+              <label class="synth-label" for="att-email">Mailbox</label>
+              <input id="att-email" name="attEmail" class="synth-input !py-1.5" [(ngModel)]="attachEmail" autocomplete="off" placeholder="name&#64;domain">
+              <label class="synth-label" for="att-pw">Its password</label>
+              <input id="att-pw" name="attPw" type="password" class="synth-input !py-1.5" [(ngModel)]="attachPassword" autocomplete="off">
+              <button type="submit" class="cyber-btn w-full py-1.5 rounded-lg text-xs font-bold"><mat-icon>link</mat-icon> ADD</button>
+            </form>
+          }
+
           <a routerLink="/compose" class="cyber-btn w-full py-2.5 rounded-xl font-bold text-xs mb-4" (click)="menuOpen.set(false)">
             <mat-icon>edit</mat-icon> COMPOSE
           </a>
@@ -165,6 +203,11 @@ export class ShellComponent {
 
   readonly themes = THEMES;
   readonly menuOpen = signal(false);
+  /** own, shared and attached mailboxes of the login (shown when there is more than the own one, or to add one) */
+  readonly boxes = signal<MailboxEntry[]>([]);
+  readonly attachOpen = signal(false);
+  attachEmail = '';
+  attachPassword = '';
   query = '';
 
   readonly links = [
@@ -195,7 +238,8 @@ export class ShellComponent {
   constructor() {
     this.state.refreshFolders();
     this.state.refreshProfile();
-    const timer = setInterval(() => this.state.refreshFolders(), 30000);
+    this.loadBoxes();
+    const timer = setInterval(() => { this.state.refreshFolders(); this.loadBoxes(); }, 30000);
     inject(DestroyRef).onDestroy(() => clearInterval(timer));
     this.router.events.pipe(filter(e => e instanceof NavigationEnd)).subscribe(() => {
       const q = this.router.parseUrl(this.router.url).queryParams['q'];
@@ -256,6 +300,52 @@ export class ShellComponent {
     }
   }
 
+  loadBoxes(): void {
+    this.api.myMailboxes().subscribe({ next: list => this.boxes.set(list), error: () => {} });
+  }
+
+  /** Another mailbox of this login: its session, full reload — fresh folders and profile. */
+  switchTo(b: MailboxEntry): void {
+    if (b.email === this.auth.email()) { this.router.navigate(['/']); return; }
+    this.api.mailboxSession(b.email).subscribe({
+      next: session => { this.state.reset(); this.auth.switchTo(session); location.assign('/'); },
+      error: e => this.toasts.error(errorText(e))
+    });
+  }
+
+  attach(): void {
+    const email = this.attachEmail.trim().toLowerCase();
+    if (!email || !this.attachPassword) { this.toasts.error('Mailbox and its password'); return; }
+    this.api.attachMailbox(email, this.attachPassword).subscribe({
+      next: b => {
+        this.attachEmail = this.attachPassword = '';
+        this.attachOpen.set(false);
+        this.toasts.ok(b.email + ' added to your mailboxes');
+        this.loadBoxes();
+      },
+      error: e => this.toasts.error(errorText(e))
+    });
+  }
+
+  leave(b: MailboxEntry): void {
+    this.dialogs.confirm(`Remove ${b.email}?`, b.shared
+      ? 'It disappears from your menu. An administrator can give it back.'
+      : 'It disappears from your menu. Add it again with its password.', 'Remove', true).subscribe(ok => {
+      if (ok === null) return;
+      this.api.leaveMailbox(b.email).subscribe({
+        next: () => {
+          this.toasts.ok(b.email + ' removed');
+          if (b.email === this.auth.email()) {
+            const own = this.boxes().find(x => x.kind === 'OWN');
+            if (own) { this.switchTo(own); return; }
+          }
+          this.loadBoxes();
+        },
+        error: e => this.toasts.error(errorText(e))
+      });
+    });
+  }
+
   backToAdmin(): void {
     this.auth.backToAdmin();
     location.assign('/settings');