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/MetricCard.tsx

@@ -0,0 +1,30 @@
+import type { LucideIcon } from "lucide-react";
+import { Card, CardContent } from "@/components/ui/card";
+
+interface MetricCardProps {
+  icon: LucideIcon;
+  value: string | number;
+  label: string;
+  description?: string;
+}
+
+export function MetricCard({ icon: Icon, value, label, description }: MetricCardProps) {
+  return (
+    <Card>
+      <CardContent className="p-4">
+        <div className="flex items-center gap-3">
+          <div className="rounded-md bg-muted p-2">
+            <Icon className="h-4 w-4 text-muted-foreground" />
+          </div>
+          <div className="flex-1 min-w-0">
+            <p className="text-2xl font-bold">{value}</p>
+            <p className="text-sm text-muted-foreground">{label}</p>
+          </div>
+        </div>
+        {description && (
+          <p className="text-xs text-muted-foreground mt-2">{description}</p>
+        )}
+      </CardContent>
+    </Card>
+  );
+}