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/CompanySwitcher.tsx

@@ -0,0 +1,57 @@
+import { ChevronsUpDown, Plus } from "lucide-react";
+import { useCompany } from "../context/CompanyContext";
+import {
+  DropdownMenu,
+  DropdownMenuContent,
+  DropdownMenuItem,
+  DropdownMenuLabel,
+  DropdownMenuSeparator,
+  DropdownMenuTrigger,
+} from "@/components/ui/dropdown-menu";
+import { Button } from "@/components/ui/button";
+
+export function CompanySwitcher() {
+  const { companies, selectedCompany, setSelectedCompanyId } = useCompany();
+
+  return (
+    <DropdownMenu>
+      <DropdownMenuTrigger asChild>
+        <Button
+          variant="ghost"
+          className="w-full justify-between px-3 py-2 h-auto text-left"
+        >
+          <div className="flex flex-col min-w-0">
+            <span className="text-xs text-muted-foreground">Company</span>
+            <span className="text-sm font-medium truncate">
+              {selectedCompany?.name ?? "Select company"}
+            </span>
+          </div>
+          <ChevronsUpDown className="h-4 w-4 shrink-0 text-muted-foreground" />
+        </Button>
+      </DropdownMenuTrigger>
+      <DropdownMenuContent align="start" className="w-[220px]">
+        <DropdownMenuLabel>Companies</DropdownMenuLabel>
+        <DropdownMenuSeparator />
+        {companies.map((company) => (
+          <DropdownMenuItem
+            key={company.id}
+            onClick={() => setSelectedCompanyId(company.id)}
+            className={company.id === selectedCompany?.id ? "bg-accent" : ""}
+          >
+            <span className="truncate">{company.name}</span>
+          </DropdownMenuItem>
+        ))}
+        {companies.length === 0 && (
+          <DropdownMenuItem disabled>No companies</DropdownMenuItem>
+        )}
+        <DropdownMenuSeparator />
+        <DropdownMenuItem asChild>
+          <a href="/companies" className="flex items-center gap-2">
+            <Plus className="h-4 w-4" />
+            Manage Companies
+          </a>
+        </DropdownMenuItem>
+      </DropdownMenuContent>
+    </DropdownMenu>
+  );
+}