Implement SimpleNote Web API - full REST API with Express

- Express server with CORS, JSON middleware
- Auth middleware (Bearer token)
- Document CRUD with markdown storage
- Library CRUD with nested support
- Tag indexing and search
- Error handler middleware
- Config from env vars
- Init script for data structure

.env.example

@@ -0,0 +1,18 @@
+# ============ SERVER ============
+PORT=3000
+HOST=0.0.0.0
+
+# ============ DATA ============
+DATA_ROOT=./data
+
+# ============ AUTH ============
+ADMIN_TOKEN=snk_initial_admin_token_change_me
+
+# ============ LOGGING ============
+LOG_LEVEL=info
+
+# ============ CORS ============
+CORS_ORIGIN=*
+
+# ============ API ============
+API_PREFIX=/api/v1