Add shared UI primitives, contexts, and reusable components

Add shadcn components: avatar, breadcrumb, checkbox, collapsible,
command, dialog, dropdown-menu, label, popover, scroll-area, sheet,
skeleton, tabs, textarea, tooltip. Add shared components: BreadcrumbBar,
CommandPalette, CompanySwitcher, CommentThread, EmptyState, EntityRow,
FilterBar, InlineEditor, MetricCard, PageSkeleton, PriorityIcon,
PropertiesPanel, StatusIcon, SidebarNavItem/Section. Add contexts for
breadcrumbs, dialogs, and side panels. Add keyboard shortcut hook and
utility helpers. Update layout, sidebar, and main app shell.

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

ui/src/components/PageSkeleton.tsx

@@ -0,0 +1,43 @@
+import { Skeleton } from "@/components/ui/skeleton";
+
+interface PageSkeletonProps {
+  variant?: "list" | "detail";
+}
+
+export function PageSkeleton({ variant = "list" }: PageSkeletonProps) {
+  if (variant === "detail") {
+    return (
+      <div className="space-y-6">
+        <div className="space-y-2">
+          <Skeleton className="h-4 w-24" />
+          <Skeleton className="h-8 w-64" />
+          <Skeleton className="h-4 w-full max-w-md" />
+        </div>
+        <div className="space-y-3">
+          <Skeleton className="h-10 w-full" />
+          <Skeleton className="h-32 w-full" />
+        </div>
+        <div className="space-y-2">
+          <Skeleton className="h-4 w-32" />
+          <Skeleton className="h-20 w-full" />
+          <Skeleton className="h-20 w-full" />
+        </div>
+      </div>
+    );
+  }
+
+  return (
+    <div className="space-y-4">
+      <div className="flex items-center justify-between">
+        <Skeleton className="h-6 w-32" />
+        <Skeleton className="h-8 w-24" />
+      </div>
+      <Skeleton className="h-10 w-full max-w-sm" />
+      <div className="space-y-1">
+        {Array.from({ length: 8 }).map((_, i) => (
+          <Skeleton key={i} className="h-10 w-full" />
+        ))}
+      </div>
+    </div>
+  );
+}