Fix feedback buttons showing "th" instead of thumbs up/down

Replace mat-icon ligatures (thumb_up/thumb_down) with emoji since
the Material Icons font is not loaded in the app. Remove unused
MatIconModule import.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/client/src/app/pages/ai-chat/ai-chat-page.component.ts

@@ -13,7 +13,6 @@ import {
 } from '@angular/core';
 import { FormsModule } from '@angular/forms';
 import { MatButtonModule } from '@angular/material/button';
-import { MatIconModule } from '@angular/material/icon';
 import { MatInputModule } from '@angular/material/input';
 import { MatProgressSpinnerModule } from '@angular/material/progress-spinner';
 import { Subject, takeUntil } from 'rxjs';
@@ -32,7 +31,6 @@ interface ChatMessage {
     CommonModule,
     FormsModule,
     MatButtonModule,
-    MatIconModule,
     MatInputModule,
     MatProgressSpinnerModule
   ],

apps/client/src/app/pages/ai-chat/ai-chat-page.html

@@ -40,7 +40,7 @@
                 [disabled]="!!msg.feedback"
                 (click)="submitFeedback(msg, 1)"
               >
-                <mat-icon>thumb_up</mat-icon>
+                👍
               </button>
               <button
                 class="feedback-btn"
@@ -50,7 +50,7 @@
                 [disabled]="!!msg.feedback"
                 (click)="submitFeedback(msg, -1)"
               >
-                <mat-icon>thumb_down</mat-icon>
+                👎
               </button>
             </div>
           }