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/SidebarSection.tsx

@@ -0,0 +1,40 @@
+import { ChevronRight, type LucideIcon } from "lucide-react";
+import { useState, type ReactNode } from "react";
+import { cn } from "../lib/utils";
+import {
+  Collapsible,
+  CollapsibleContent,
+  CollapsibleTrigger,
+} from "@/components/ui/collapsible";
+
+interface SidebarSectionProps {
+  label: string;
+  icon?: LucideIcon;
+  children: ReactNode;
+  defaultOpen?: boolean;
+}
+
+export function SidebarSection({
+  label,
+  children,
+  defaultOpen = true,
+}: SidebarSectionProps) {
+  const [open, setOpen] = useState(defaultOpen);
+
+  return (
+    <Collapsible open={open} onOpenChange={setOpen}>
+      <CollapsibleTrigger className="flex items-center gap-1 w-full px-3 py-1.5 text-xs font-semibold uppercase tracking-wider text-muted-foreground hover:text-foreground transition-colors">
+        <ChevronRight
+          className={cn(
+            "h-3 w-3 transition-transform",
+            open && "rotate-90"
+          )}
+        />
+        {label}
+      </CollapsibleTrigger>
+      <CollapsibleContent>
+        <div className="flex flex-col gap-0.5 mt-0.5">{children}</div>
+      </CollapsibleContent>
+    </Collapsible>
+  );
+}