feat(design-system): add reusable Dialog primitive

Standalone, OnPush. Backdrop click and Escape close, focus trap with
return-focus on close, role=dialog/aria-modal. Sizes sm/md/lg. Colors/
radius/shadow/spacing via existing tenant CSS vars with fallbacks.

src/app/shared/ui/dialog/dialog.component.scss

@@ -0,0 +1,104 @@
+.app-dialog-backdrop {
+  position: fixed;
+  inset: 0;
+  z-index: 1000;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  padding: var(--space-md, 1rem);
+  background: rgba(0, 0, 0, 0.5);
+  animation: app-dialog-fade-in var(--transition-normal, 200ms ease);
+}
+
+.app-dialog-panel {
+  width: 100%;
+  max-height: 90vh;
+  overflow-y: auto;
+  background: var(--bg-primary, #fff);
+  border-radius: var(--radius-lg, 10px);
+  box-shadow: var(--shadow-md, 0 8px 24px rgba(0, 0, 0, 0.16));
+  animation: app-dialog-scale-in var(--transition-normal, 200ms ease);
+
+  &:focus-visible {
+    outline: none;
+  }
+}
+
+.app-dialog-panel--sm {
+  max-width: 400px;
+}
+
+.app-dialog-panel--md {
+  max-width: 560px;
+}
+
+.app-dialog-panel--lg {
+  max-width: 800px;
+}
+
+.app-dialog-panel__header {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: var(--space-md, 1rem);
+  padding: var(--space-md, 1rem) var(--space-lg, 1.5rem);
+  border-bottom: 1px solid var(--border-color, #e4e4e7);
+}
+
+.app-dialog-panel__title {
+  margin: 0;
+  font-size: 1.125rem;
+  font-weight: 600;
+  color: var(--text-primary, #1f322d);
+}
+
+.app-dialog-panel__close {
+  border: none;
+  background: transparent;
+  color: var(--text-secondary, #6b7280);
+  font-size: 1.5rem;
+  line-height: 1;
+  cursor: pointer;
+  padding: var(--space-xs, 0.25rem);
+  border-radius: var(--radius-sm, 4px);
+
+  &:hover {
+    background: var(--bg-secondary, #f4f4f5);
+  }
+
+  &:focus-visible {
+    outline: 2px solid var(--primary-color, #2f6e5d);
+    outline-offset: 2px;
+  }
+}
+
+.app-dialog-panel__body {
+  padding: var(--space-lg, 1.5rem);
+}
+
+@keyframes app-dialog-fade-in {
+  from {
+    opacity: 0;
+  }
+  to {
+    opacity: 1;
+  }
+}
+
+@keyframes app-dialog-scale-in {
+  from {
+    opacity: 0;
+    transform: scale(0.96);
+  }
+  to {
+    opacity: 1;
+    transform: scale(1);
+  }
+}
+
+@media (prefers-reduced-motion: reduce) {
+  .app-dialog-backdrop,
+  .app-dialog-panel {
+    animation: none;
+  }
+}