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/context/BreadcrumbContext.tsx

@@ -0,0 +1,35 @@
+import { createContext, useCallback, useContext, useState, type ReactNode } from "react";
+
+export interface Breadcrumb {
+  label: string;
+  href?: string;
+}
+
+interface BreadcrumbContextValue {
+  breadcrumbs: Breadcrumb[];
+  setBreadcrumbs: (crumbs: Breadcrumb[]) => void;
+}
+
+const BreadcrumbContext = createContext<BreadcrumbContextValue | null>(null);
+
+export function BreadcrumbProvider({ children }: { children: ReactNode }) {
+  const [breadcrumbs, setBreadcrumbsState] = useState<Breadcrumb[]>([]);
+
+  const setBreadcrumbs = useCallback((crumbs: Breadcrumb[]) => {
+    setBreadcrumbsState(crumbs);
+  }, []);
+
+  return (
+    <BreadcrumbContext.Provider value={{ breadcrumbs, setBreadcrumbs }}>
+      {children}
+    </BreadcrumbContext.Provider>
+  );
+}
+
+export function useBreadcrumbs() {
+  const ctx = useContext(BreadcrumbContext);
+  if (!ctx) {
+    throw new Error("useBreadcrumbs must be used within BreadcrumbProvider");
+  }
+  return ctx;
+}