feat: make gateway publishable + add npmjs publish script

- Remove `private: true` from gateway package.json
- Add bin entry (mosaic-gateway), files array, npmjs publishConfig
- Add shebang to main.ts for bin execution
- New scripts/publish-npmjs.sh that patches @mosaic/* → @mosaicstack/*,
  resolves workspace deps to real versions, publishes to npmjs, restores
- Add publish-npmjs CI step in Woodpecker (runs on tags only)
- Update Gitea publish step comments for clarity

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/gateway/package.json

@@ -1,9 +1,18 @@
 {
   "name": "@mosaic/gateway",
   "version": "0.0.2",
-  "private": true,
   "type": "module",
   "main": "dist/main.js",
+  "bin": {
+    "mosaic-gateway": "dist/main.js"
+  },
+  "files": [
+    "dist"
+  ],
+  "publishConfig": {
+    "registry": "https://registry.npmjs.org/",
+    "access": "public"
+  },
   "scripts": {
     "build": "tsc",
     "dev": "tsx watch src/main.ts",

apps/gateway/src/main.ts

@@ -1,3 +1,4 @@
+#!/usr/bin/env node
 import { config } from 'dotenv';
 import { existsSync } from 'node:fs';
 import { resolve, join } from 'node:path';