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>

crates/vault-scheduler/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "vault-scheduler"
+version.workspace = true
+edition.workspace = true
+
+[dependencies]
+vault-core.workspace = true
+vault-watch.workspace = true
+tokio.workspace = true
+cron.workspace = true
+chrono.workspace = true
+tracing.workspace = true
+thiserror.workspace = true
+async-trait.workspace = true
+reqwest.workspace = true
+serde.workspace = true
+serde_json.workspace = true
+serde_yaml.workspace = true
+uuid.workspace = true