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>

install.sh

@@ -0,0 +1,28 @@
+#!/usr/bin/env sh
+# Bootstrap installer for ClaudeMailbox on macOS / Linux.
+#
+# Usage:
+#   curl -fsSL https://git.kuns.dev/releases/ClaudeMailbox/raw/branch/main/install.sh | sh
+#
+# Env vars:
+#   NO_AUTOSTART=1   skip install-autostart
+set -eu
+
+if ! command -v npm >/dev/null 2>&1; then
+  echo "error: Node.js / npm not found on PATH. Install Node 20+ from https://nodejs.org and retry." >&2
+  exit 1
+fi
+
+echo "Configuring @kuns scoped npm registry..."
+npm config set "@kuns:registry" "https://git.kuns.dev/api/packages/releases/npm/"
+
+echo "Installing @kuns/claude-mailbox globally..."
+npm install -g "@kuns/claude-mailbox"
+
+if [ -z "${NO_AUTOSTART:-}" ]; then
+  echo "Registering autostart..."
+  claude-mailbox install-autostart
+fi
+
+echo ""
+echo "ClaudeMailbox installed. Run 'claude-mailbox status' to verify."