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/routes/skills.rs

@@ -0,0 +1,62 @@
+use crate::error::ApiError;
+use crate::state::AppState;
+use axum::extract::{Path, State};
+use axum::routing::get;
+use axum::{Json, Router};
+use serde_json::{json, Value};
+use std::sync::Arc;
+
+pub fn routes() -> Router<Arc<AppState>> {
+    Router::new()
+        .route("/skills", get(list_skills))
+        .route("/skills/{name}", get(get_skill))
+        .route("/skills/{name}/used-by", get(skill_used_by))
+}
+
+async fn list_skills(State(state): State<Arc<AppState>>) -> Result<Json<Value>, ApiError> {
+    let skills = state.skills.read().unwrap();
+    let list: Vec<Value> = skills
+        .values()
+        .map(|s| {
+            json!({
+                "name": s.frontmatter.name,
+                "description": s.frontmatter.description,
+                "version": s.frontmatter.version,
+            })
+        })
+        .collect();
+    Ok(Json(json!(list)))
+}
+
+async fn get_skill(
+    State(state): State<Arc<AppState>>,
+    Path(name): Path<String>,
+) -> Result<Json<Value>, ApiError> {
+    let skills = state.skills.read().unwrap();
+    let skill = skills
+        .get(&name)
+        .ok_or_else(|| ApiError::NotFound(format!("Skill '{}' not found", name)))?;
+
+    Ok(Json(json!({
+        "name": skill.frontmatter.name,
+        "description": skill.frontmatter.description,
+        "version": skill.frontmatter.version,
+        "requires_mcp": skill.frontmatter.requires_mcp,
+        "inputs": skill.frontmatter.inputs,
+        "outputs": skill.frontmatter.outputs,
+        "body": skill.body,
+    })))
+}
+
+async fn skill_used_by(
+    State(state): State<Arc<AppState>>,
+    Path(name): Path<String>,
+) -> Result<Json<Value>, ApiError> {
+    let agents = state.agents.read().unwrap();
+    let users: Vec<String> = agents
+        .values()
+        .filter(|a| a.frontmatter.skills.contains(&name))
+        .map(|a| a.frontmatter.name.clone())
+        .collect();
+    Ok(Json(json!(users)))
+}