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-api/src/lib.rs

@@ -0,0 +1,28 @@
+pub mod error;
+pub mod routes;
+pub mod state;
+pub mod ws;
+pub mod ws_protocol;
+
+use axum::Router;
+use std::sync::Arc;
+use tower_http::cors::{Any, CorsLayer};
+use tower_http::trace::TraceLayer;
+
+pub use state::AppState;
+
+pub fn build_router(state: Arc<AppState>) -> Router {
+    let cors = CorsLayer::new()
+        .allow_origin(Any)
+        .allow_methods(Any)
+        .allow_headers(Any);
+
+    let api = routes::api_routes();
+
+    Router::new()
+        .nest("/api", api)
+        .route("/ws", axum::routing::get(ws::ws_handler))
+        .layer(cors)
+        .layer(TraceLayer::new_for_http())
+        .with_state(state)
+}