fix: add private:true to packages not meant for npm (#345)

* fix(ci): run on all PRs with conditional skip

- Remove paths filter from pull_request trigger
- Add check-changes job to detect code changes
- Skip full CI if no code files changed
- Satisfies branch protection while avoiding unnecessary builds

* fix: add private:true to packages not meant for npm

Prevents changesets from trying to publish internal packages:
- engine/* (8 packages)
- rendering/* (8 packages)
- physics/* (2 packages)
- streaming/* (1 package)
- tools/sdk, tools/worker-generator

packages/engine/platform-web/package.json

@@ -57,5 +57,6 @@
     "type": "git",
     "url": "https://github.com/esengine/esengine.git",
     "directory": "packages/platform-web"
-  }
+  },
+  "private": true
 }