fix: scope Gitea registry to @mosaic packages only during gateway install

The --registry flag overrides all package resolution, causing npm to
look for third-party deps (e.g. @anthropic-ai/sdk) on Gitea. Fix by
writing a scoped .npmrc that routes only @mosaic/* to Gitea while
letting everything else resolve from npmjs normally.

Bump to 0.0.13.

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

packages/mosaic/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@mosaic/mosaic",
-  "version": "0.0.12",
+  "version": "0.0.13",
   "repository": {
     "type": "git",
     "url": "https://git.mosaicstack.dev/mosaic/mosaic-stack.git",