fix(auth): clarify admin login flow

Use admin-specific Telegram copy and define the missing credential API. Replace predictable bootstrap passwords with random one-time secrets.

src/app/components/telegram-login/telegram-login.component.html

@@ -9,8 +9,8 @@
         <app-icon name="lock" [size]="40" />
       </div>
 
-      <h2>{{ 'auth.loginRequired' | translate }}</h2>
-      <p class="login-desc">{{ 'auth.loginDescription' | translate }}</p>
+      <h2>{{ (mode === 'admin' ? 'auth.adminLoginRequired' : 'auth.loginRequired') | translate }}</h2>
+      <p class="login-desc">{{ (mode === 'admin' ? 'auth.adminLoginDescription' : 'auth.loginDescription') | translate }}</p>
 
       @if (status() === 'checking') {
         <div class="login-status checking">
@@ -22,7 +22,7 @@
           <svg class="tg-icon" width="22" height="22" viewBox="0 0 24 24" fill="currentColor">
             <path d="M11.944 0A12 12 0 0 0 0 12a12 12 0 0 0 12 12 12 12 0 0 0 12-12A12 12 0 0 0 12 0a12 12 0 0 0-.056 0zm4.962 7.224c.1-.002.321.023.465.14a.506.506 0 0 1 .171.325c.016.093.036.306.02.472-.18 1.898-.962 6.502-1.36 8.627-.168.9-.499 1.201-.82 1.23-.696.065-1.225-.46-1.9-.902-1.056-.693-1.653-1.124-2.678-1.8-1.185-.78-.417-1.21.258-1.91.177-.184 3.247-2.977 3.307-3.23.007-.032.014-.15-.056-.212s-.174-.041-.249-.024c-.106.024-1.793 1.14-5.061 3.345-.48.33-.913.49-1.302.48-.428-.008-1.252-.241-1.865-.44-.752-.245-1.349-.374-1.297-.789.027-.216.325-.437.893-.663 3.498-1.524 5.83-2.529 6.998-3.014 3.332-1.386 4.025-1.627 4.476-1.635z"/>
           </svg>
-          {{ 'auth.loginWithTelegram' | translate }}
+          {{ (mode === 'admin' ? 'auth.adminLoginWithTelegram' : 'auth.loginWithTelegram') | translate }}
         </button>
 
         <!-- @if (loginUrl()) {
@@ -64,7 +64,7 @@
           }
         </div>
 
-        <p class="login-note">{{ 'auth.loginNote' | translate }}</p>
+        <p class="login-note">{{ (mode === 'admin' ? 'auth.adminLoginNote' : 'auth.loginNote') | translate }}</p>
       }
     </div>
   </div>