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/EmptyState.tsx

@@ -0,0 +1,23 @@
+import type { LucideIcon } from "lucide-react";
+import { Button } from "@/components/ui/button";
+
+interface EmptyStateProps {
+  icon: LucideIcon;
+  message: string;
+  action?: string;
+  onAction?: () => void;
+}
+
+export function EmptyState({ icon: Icon, message, action, onAction }: EmptyStateProps) {
+  return (
+    <div className="flex flex-col items-center justify-center py-16 text-center">
+      <Icon className="h-12 w-12 text-muted-foreground/50 mb-4" />
+      <p className="text-sm text-muted-foreground mb-4">{message}</p>
+      {action && onAction && (
+        <Button variant="outline" size="sm" onClick={onAction}>
+          {action}
+        </Button>
+      )}
+    </div>
+  );
+}