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/index.css

@@ -0,0 +1,24 @@
+@import "tailwindcss";
+
+@theme {
+  --color-surface: #0f1117;
+  --color-surface-raised: #1a1d27;
+  --color-surface-overlay: #252833;
+  --color-border: #2e3241;
+  --color-border-hover: #3d4254;
+  --color-text-primary: #e1e4ed;
+  --color-text-secondary: #8b90a0;
+  --color-text-muted: #5c6070;
+  --color-accent: #6c8cff;
+  --color-accent-hover: #8aa3ff;
+  --color-success: #4ade80;
+  --color-warning: #fbbf24;
+  --color-danger: #f87171;
+  --color-urgent: #ef4444;
+}
+
+body {
+  @apply bg-surface text-text-primary;
+  margin: 0;
+  font-family: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
+}