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/SidebarNavItem.tsx

@@ -0,0 +1,42 @@
+import { NavLink } from "react-router-dom";
+import { cn } from "../lib/utils";
+import type { LucideIcon } from "lucide-react";
+
+interface SidebarNavItemProps {
+  to: string;
+  label: string;
+  icon: LucideIcon;
+  end?: boolean;
+  badge?: number;
+}
+
+export function SidebarNavItem({
+  to,
+  label,
+  icon: Icon,
+  end,
+  badge,
+}: SidebarNavItemProps) {
+  return (
+    <NavLink
+      to={to}
+      end={end}
+      className={({ isActive }) =>
+        cn(
+          "flex items-center gap-2 px-3 py-1.5 rounded-md text-sm font-medium transition-colors",
+          isActive
+            ? "bg-accent text-accent-foreground"
+            : "text-muted-foreground hover:bg-accent/50 hover:text-accent-foreground"
+        )
+      }
+    >
+      <Icon className="h-4 w-4 shrink-0" />
+      <span className="flex-1 truncate">{label}</span>
+      {badge != null && badge > 0 && (
+        <span className="ml-auto text-xs bg-primary text-primary-foreground rounded-full px-1.5 py-0.5 leading-none">
+          {badge}
+        </span>
+      )}
+    </NavLink>
+  );
+}