feat(node): add TypeScript sibling project for npm-based install

Introduces @kuns/claude-mailbox under node/, a wire-compatible TypeScript
port of the .NET daemon that distributes via the public Gitea npm registry.
The .NET project stays in src/ClaudeMailbox/ untouched; users pick whichever
flavor they prefer.

- node/ project: fastify + @modelcontextprotocol/sdk StreamableHTTPServerTransport
  + better-sqlite3, schema and wire surface match the C# version (port 47822,
  X-Mailbox header, MCP tool names, snake_case SQLite columns)
- Cross-platform autostart: Scheduled Task (Win, no admin) / Windows Service
  (Win, --service) / launchd (mac) / systemd --user (linux)
- 9/9 vitest tests pass; end-to-end /health + send/check round-trip verified
- CI split: existing ci.yml/release.yml renamed to *-dotnet.yml with path
  filters, new ci-node.yml and release-node.yml publish to Gitea npm registry
- install.ps1 / install.sh bootstrap one-liners at repo root; homebrew/
  contains a tap formula template
- README install section reordered: npm path primary, dotnet publish secondary

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

node/README.md

@@ -0,0 +1,20 @@
+# @kuns/claude-mailbox
+
+Standalone MCP mail server that lets parallel Claude sessions coordinate with each other. TypeScript / Node port of the .NET `claude-mailbox` daemon — wire-compatible (same port, same `X-Mailbox` header, same MCP tool names, same SQLite schema).
+
+## Install
+
+One-time per machine:
+
+```sh
+npm config set @kuns:registry=https://git.kuns.dev/api/packages/releases/npm/
+npm install -g @kuns/claude-mailbox
+```
+
+Then:
+
+```sh
+claude-mailbox install-autostart   # registers per-OS autostart, no admin needed by default
+```
+
+See the repository [README](../README.md) for the full architecture, MCP tool reference, and `.mcp.json` snippet.