Add npm package for bd with native binaries (bd-febc)

Implements @beads/bd npm package for easy installation in Node.js
environments, especially Claude Code for Web.

Features:
- Automatic platform-specific binary download during postinstall
- CLI wrapper that invokes native bd binary
- Full feature parity with standalone bd
- Works with SessionStart hooks for auto-installation

Package structure:
- bin/bd.js: Node.js CLI wrapper
- scripts/postinstall.js: Downloads correct binary from GitHub releases
- scripts/test.js: Verification tests
- Comprehensive documentation (6 guides)

Published to npm: https://www.npmjs.com/package/@beads/bd

Benefits vs WASM:
- Full SQLite support (no custom VFS)
- Better performance (native vs WASM)
- Simpler implementation and maintenance
- All commands work identically

Closes bd-febc, bd-be7a, bd-e2e6, bd-f282, bd-87a0, bd-b54c

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

README.md

@@ -2,6 +2,7 @@
 
 [![Go Version](https://img.shields.io/github/go-mod/go-version/steveyegge/beads)](https://go.dev/)
 [![Release](https://img.shields.io/github/v/release/steveyegge/beads)](https://github.com/steveyegge/beads/releases)
+[![npm version](https://img.shields.io/npm/v/@beads/bd)](https://www.npmjs.com/package/@beads/bd)
 [![CI](https://img.shields.io/github/actions/workflow/status/steveyegge/beads/ci.yml?branch=main&label=tests)](https://github.com/steveyegge/beads/actions/workflows/ci.yml)
 [![Go Report Card](https://goreportcard.com/badge/github.com/steveyegge/beads)](https://goreportcard.com/report/github.com/steveyegge/beads)
 [![License](https://img.shields.io/github/license/steveyegge/beads)](LICENSE)
@@ -67,6 +68,11 @@ Agents report that they enjoy working with Beads, and they will use it spontaneo
 
 ## Installation
 
+**npm (Node.js environments, Claude Code for Web):**
+```bash
+npm install -g @beads/bd
+```
+
 **Quick install (all platforms):**
 ```bash
 curl -fsSL https://raw.githubusercontent.com/steveyegge/beads/main/scripts/install.sh | bash
@@ -82,6 +88,8 @@ brew install bd
 
 **IDE Integration:** See [INSTALLING.md](INSTALLING.md) for Claude Code plugin and MCP server setup.
 
+**Claude Code for Web:** See [npm-package/CLAUDE_CODE_WEB.md](npm-package/CLAUDE_CODE_WEB.md) for SessionStart hook setup.
+
 ## Quick Start
 
 ### For Humans