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/PropertiesPanel.tsx

@@ -0,0 +1,24 @@
+import { X } from "lucide-react";
+import { usePanel } from "../context/PanelContext";
+import { Button } from "@/components/ui/button";
+import { ScrollArea } from "@/components/ui/scroll-area";
+
+export function PropertiesPanel() {
+  const { panelContent, closePanel } = usePanel();
+
+  if (!panelContent) return null;
+
+  return (
+    <aside className="w-80 border-l border-border bg-card flex flex-col shrink-0">
+      <div className="flex items-center justify-between px-4 py-2 border-b border-border">
+        <span className="text-sm font-medium">Properties</span>
+        <Button variant="ghost" size="icon-xs" onClick={closePanel}>
+          <X className="h-4 w-4" />
+        </Button>
+      </div>
+      <ScrollArea className="flex-1">
+        <div className="p-4">{panelContent}</div>
+      </ScrollArea>
+    </aside>
+  );
+}