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.scss

@@ -0,0 +1,87 @@
+:host {
+  display: contents;
+}
+
+.modal-shell {
+  position: fixed;
+  inset: 0;
+  z-index: 2000;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  padding: 1rem;
+  background: rgba(16, 18, 22, 0.48);
+  backdrop-filter: blur(2px);
+}
+
+.modal-shell__dialog {
+  width: min(100%, 40rem);
+  margin: 0;
+}
+
+.modal-shell__dialog.modal-sm {
+  width: min(100%, 24rem);
+}
+
+.modal-shell__dialog.modal-lg {
+  width: min(100%, 52rem);
+}
+
+.modal-shell__dialog.modal-xl {
+  width: min(100%, 68rem);
+}
+
+.modal-shell__dialog--full {
+  width: min(100%, 92rem);
+  height: min(100%, calc(100dvh - 2rem));
+}
+
+.modal-shell__content {
+  max-height: calc(100dvh - 2rem);
+  border-radius: 1.25rem;
+  background:
+    linear-gradient(180deg, rgba(255, 255, 255, 0.98), rgba(248, 248, 248, 0.98));
+}
+
+.modal-shell__dialog--full .modal-shell__content {
+  height: 100%;
+  max-height: 100%;
+}
+
+.modal-shell__header {
+  align-items: flex-start;
+  padding: 1.25rem 1.25rem 0.75rem;
+}
+
+.modal-shell__title {
+  margin: 0;
+  font-size: clamp(1.15rem, 1rem + 0.4vw, 1.5rem);
+  font-weight: 700;
+  line-height: 1.15;
+  color: #202020;
+}
+
+.modal-shell__body {
+  padding: 0 1.25rem 1.25rem;
+  color: #303030;
+}
+
+@media (max-width: 576px) {
+  .modal-shell {
+    padding: 0.75rem;
+    align-items: flex-end;
+  }
+
+  .modal-shell__dialog,
+  .modal-shell__dialog.modal-sm,
+  .modal-shell__dialog.modal-lg,
+  .modal-shell__dialog.modal-xl,
+  .modal-shell__dialog--full {
+    width: 100%;
+  }
+
+  .modal-shell__content {
+    max-height: min(100dvh - 1.5rem, 48rem);
+    border-radius: 1.25rem 1.25rem 0.75rem 0.75rem;
+  }
+}