fix(frontend): center delete-all, rework keyboard shortcuts, add preview backdrop

- Center 'Delete All Forms' button and add bottom padding
- Search shortcut: Shift+K -> Ctrl/Cmd+K
- Form navigation: Ctrl/Cmd+J/K -> Shift+J/K (frees Ctrl/Cmd+K for search)
- Keep navbar title centered when preview actions appear
- Add dark backdrop that blocks background clicks when form preview is open
- Center close + form action icons inside their icon buttons

frontend/src/app/components/form-list/form-list.component.ts

@@ -83,9 +83,9 @@ import { FormData } from '../../services/form.service';
     }
 
     .delete-all-wrapper {
-      padding: 0.5rem 1rem 0.5rem 1rem;
+      padding: 0.5rem 1rem 1.25rem 1rem;
       display: flex;
-      justify-content: flex-end;
+      justify-content: center;
     }
 
     .form-item {
@@ -160,6 +160,27 @@ import { FormData } from '../../services/form.service';
         align-items: center;
         gap: 0.25rem;
         flex-shrink: 0;
+
+        ::ng-deep .mat-mdc-icon-button {
+          display: inline-flex;
+          align-items: center;
+          justify-content: center;
+          width: 40px;
+          height: 40px;
+          padding: 0;
+          line-height: 1;
+
+          .mat-icon {
+            display: inline-flex;
+            align-items: center;
+            justify-content: center;
+            width: 24px;
+            height: 24px;
+            font-size: 24px;
+            line-height: 1;
+            margin: 0;
+          }
+        }
       }
     }
   `]

frontend/src/app/components/navbar/navbar.component.ts

@@ -25,7 +25,7 @@ import { Subscription } from 'rxjs';
 
       <div class="navbar-actions" *ngIf="selectedFormDetails">
         <div class="keyboard-shortcuts">
-          <span class="shortcut-hint">Ctrl+J/K: forms • Ctrl+Shift+J/K: questions • Esc: exit</span>
+          <span class="shortcut-hint">Shift+J/K: forms • Ctrl+Shift+J/K: questions • Esc: exit</span>
         </div>
         <button mat-icon-button (click)="closePreview()" class="close-preview-btn">
           <mat-icon>close</mat-icon>
@@ -33,6 +33,11 @@ import { Subscription } from 'rxjs';
       </div>
     </mat-toolbar>
 
+    <!-- Backdrop to block background interaction when preview is open -->
+    <div class="form-preview-backdrop"
+         *ngIf="selectedFormDetails"
+         (click)="closePreview()"></div>
+
     <!-- Form Preview Panel -->
     <div class="form-preview-panel"
          [class.open]="selectedFormDetails"
@@ -109,21 +114,30 @@ import { Subscription } from 'rxjs';
       z-index: 1000;
       position: relative;
       display: flex;
-      justify-content: space-between;
+      justify-content: flex-end;
       align-items: center;
       border-bottom: 1px solid rgba(255, 255, 255, 0.2);
+      padding: 0 1rem;
     }
 
     .navbar-brand {
+      position: absolute;
+      left: 0;
+      right: 0;
+      top: 0;
+      bottom: 0;
       display: flex;
       align-items: center;
+      justify-content: center;
       gap: 0.5rem;
       font-size: 1.2rem;
       font-weight: 500;
+      pointer-events: none;
     }
 
-    .center-navbar { justify-content: center; width: 100%; display: flex; }
-    .navbar { justify-content: center; }
+    .center-navbar {
+      display: flex;
+    }
 
     .brand-icon {
       font-size: 24px;
@@ -136,6 +150,8 @@ import { Subscription } from 'rxjs';
       display: flex;
       align-items: center;
       gap: 1rem;
+      position: relative;
+      z-index: 2;
     }
 
     .keyboard-shortcuts {
@@ -153,12 +169,46 @@ import { Subscription } from 'rxjs';
     .close-preview-btn {
       background: rgba(255, 255, 255, 0.1);
       color: #ffffff;
+      display: inline-flex;
+      align-items: center;
+      justify-content: center;
+      width: 40px;
+      height: 40px;
+      line-height: 1;
+
+      ::ng-deep .mat-icon {
+        display: inline-flex;
+        align-items: center;
+        justify-content: center;
+        width: 24px;
+        height: 24px;
+        font-size: 24px;
+        line-height: 1;
+        margin: 0;
+      }
 
       &:hover {
         background: rgba(255, 255, 255, 0.2);
       }
     }
 
+    .form-preview-backdrop {
+      position: fixed;
+      top: 0;
+      left: 0;
+      right: 0;
+      bottom: 0;
+      background: rgba(0, 0, 0, 0.75);
+      backdrop-filter: blur(6px);
+      z-index: 998;
+      animation: fadeIn 0.3s ease;
+    }
+
+    @keyframes fadeIn {
+      from { opacity: 0; }
+      to { opacity: 1; }
+    }
+
     .form-preview-panel {
       position: fixed;
       top: 80px;

frontend/src/app/components/search/search.component.ts

@@ -21,7 +21,7 @@ import { MatIconModule } from '@angular/material/icon';
         <mat-icon matPrefix>search</mat-icon>
         <input #searchInput
                matInput
-               placeholder="Search forms... (Shift+K)"
+               placeholder="Search forms... (Ctrl/⌘+K)"
                [(ngModel)]="searchQuery"
                (input)="onSearch()">
       </mat-form-field>
@@ -190,8 +190,13 @@ export class SearchComponent implements OnInit, OnDestroy {
 
   @HostListener('window:keydown', ['$event'])
   handleKeyboardShortcut(event: KeyboardEvent) {
-    // Check for Shift+K
-    if (event.shiftKey && event.key.toLowerCase() === 'k') {
+    // Check for Ctrl/Cmd + K (without Shift)
+    if (
+      (event.ctrlKey || event.metaKey) &&
+      !event.shiftKey &&
+      !event.altKey &&
+      event.key.toLowerCase() === 'k'
+    ) {
       event.preventDefault();
       this.focusSearch();
     }

frontend/src/app/components/upload/upload.component.ts

@@ -1165,11 +1165,11 @@ export class UploadComponent implements OnInit, OnChanges {
 
   @HostListener('document:keydown', ['$event'])
   onKeyDown(event: KeyboardEvent): void {
-    if (event.ctrlKey || event.metaKey) {
-      if (event.key === 'j') {
+    if (event.shiftKey && !event.ctrlKey && !event.metaKey && !event.altKey) {
+      if (event.key === 'j' || event.key === 'J') {
         event.preventDefault();
         this.navigateToNextForm();
-      } else if (event.key === 'k') {
+      } else if (event.key === 'k' || event.key === 'K') {
         event.preventDefault();
         this.navigateToPreviousForm();
       }