Initial implementation of vault-os

Complete implementation across all 13 phases:

- vault-core: types, YAML frontmatter parsing, entity classification,
  filesystem ops, config, prompt composition, validation, search
- vault-watch: filesystem watcher with daemon write filtering, event
  classification
- vault-scheduler: cron engine, process executor, task runner with
  retry logic and concurrency limiting
- vault-api: Axum REST API (15 route modules), WebSocket with broadcast,
  AI assistant proxy, validation, templates
- Dashboard: React + TypeScript + Tailwind v4 with kanban, CodeMirror
  editor, dynamic view system, AI chat sidebar
- Nix flake with dev shell and NixOS module
- Graceful shutdown, inotify overflow recovery, tracing instrumentation

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

dashboard/src/components/ActivityFeed.tsx

@@ -0,0 +1,39 @@
+import { useActivity } from '../hooks/useApi';
+
+export function ActivityFeed() {
+  const { data: activity, isLoading } = useActivity();
+
+  if (isLoading) return <div className="p-4 text-sm text-text-muted">Loading...</div>;
+  if (!activity?.length) return <div className="p-4 text-sm text-text-muted">No recent activity</div>;
+
+  return (
+    <div className="space-y-1">
+      {activity.slice(0, 20).map((item, i) => (
+        <div key={i} className="flex items-center gap-2 px-4 py-1.5 text-xs">
+          <span className={`h-1.5 w-1.5 rounded-full ${kindColor(item.kind)}`} />
+          <span className="flex-1 truncate text-text-secondary">{item.name}</span>
+          <span className="text-text-muted">{timeAgo(item.modified)}</span>
+        </div>
+      ))}
+    </div>
+  );
+}
+
+function kindColor(kind: string): string {
+  switch (kind) {
+    case 'human_task': return 'bg-accent';
+    case 'agent_task': return 'bg-warning';
+    case 'knowledge': return 'bg-success';
+    default: return 'bg-text-muted';
+  }
+}
+
+function timeAgo(iso: string): string {
+  const ms = Date.now() - new Date(iso).getTime();
+  const mins = Math.floor(ms / 60000);
+  if (mins < 1) return 'now';
+  if (mins < 60) return `${mins}m`;
+  const hrs = Math.floor(mins / 60);
+  if (hrs < 24) return `${hrs}h`;
+  return `${Math.floor(hrs / 24)}d`;
+}