feat: implement modal service and components for enhanced user interaction, including modal showcase in demo page

src/app/shared/components/modal-shell/modal-shell.component.html

@@ -0,0 +1,39 @@
+<div class="modal-shell" (click)="backdropClick.emit()">
+  <div
+    class="modal-dialog modal-dialog-centered modal-dialog-scrollable modal-shell__dialog"
+    [ngClass]="dialogClass()"
+    (click)="$event.stopPropagation()"
+  >
+    <div
+      #panel
+      class="modal-content border-0 shadow-lg modal-shell__content"
+      role="dialog"
+      aria-modal="true"
+      [attr.aria-labelledby]="ariaLabelledBy"
+      tabindex="-1"
+    >
+      @if (title() || showCloseButton()) {
+        <header class="modal-header border-0 modal-shell__header">
+          @if (title()) {
+            <h2 class="modal-title modal-shell__title" [id]="titleId">{{ title() }}</h2>
+          } @else {
+            <span></span>
+          }
+
+          @if (showCloseButton()) {
+            <button
+              type="button"
+              class="btn-close"
+              aria-label="Cerrar modal"
+              (click)="closeRequested.emit()"
+            ></button>
+          }
+        </header>
+      }
+
+      <div class="modal-body modal-shell__body">
+        <ng-content />
+      </div>
+    </div>
+  </div>
+</div>