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/lib/groupBy.ts

@@ -0,0 +1,11 @@
+export function groupBy<T>(items: T[], keyFn: (item: T) => string): Record<string, T[]> {
+  const result: Record<string, T[]> = {};
+  for (const item of items) {
+    const key = keyFn(item);
+    if (!result[key]) {
+      result[key] = [];
+    }
+    result[key].push(item);
+  }
+  return result;
+}

ui/src/lib/timeAgo.ts

@@ -0,0 +1,31 @@
+const MINUTE = 60;
+const HOUR = 60 * MINUTE;
+const DAY = 24 * HOUR;
+const WEEK = 7 * DAY;
+const MONTH = 30 * DAY;
+
+export function timeAgo(date: Date | string): string {
+  const now = Date.now();
+  const then = new Date(date).getTime();
+  const seconds = Math.round((now - then) / 1000);
+
+  if (seconds < MINUTE) return "just now";
+  if (seconds < HOUR) {
+    const m = Math.floor(seconds / MINUTE);
+    return `${m}m ago`;
+  }
+  if (seconds < DAY) {
+    const h = Math.floor(seconds / HOUR);
+    return `${h}h ago`;
+  }
+  if (seconds < WEEK) {
+    const d = Math.floor(seconds / DAY);
+    return `${d}d ago`;
+  }
+  if (seconds < MONTH) {
+    const w = Math.floor(seconds / WEEK);
+    return `${w}w ago`;
+  }
+  const mo = Math.floor(seconds / MONTH);
+  return `${mo}mo ago`;
+}