Platform wide SubFlow sharing

### Description

As a FlowFuse admin
I would like to create subflows that can be accessed by all teams
So I can create reusable components that are scoped wider than a Team

Currently FlowFuse has 2 options for sharing SubFlows
1. export to library, instance or team scope
2. export subflow to npm package stored in Team level npm registry

Both these are Team scoped not platform scoped.

Would like a way to either copy (and rename) npm packages to something available to all teams or promote a Team Library entry to Platform wide Library entry.

Requesting customer:
- https://app-eu1.hubspot.com/contacts/26586079/record/0-2/8175387106?eschref=%2Fhelp-desk%2F26586079%2Fview%2F233410279%2Fticket%2F430477095138%2Fthread%2F21342732485

Initial request:
- https://app-eu1.hubspot.com/help-desk/26586079/view/233410279/ticket/430477095138/thread/21342732485?messageId=37ae47d6-af99-49d2-b662-c42c08867a3d

### Which customers would this be available to

Enterprise Tier Only (EE)

### Have you provided an initial effort estimate for this issue?

I have provided an initial effort estimate

No files, tests, or entry points are named. Start by locating the existing team-scoped SubFlow library and npm package flows, then trace how team and platform access is represented. Done means defining and implementing a platform-wide sharing path, including whether promotion or package copying is supported and restricting it to Enterprise Tier customers.

Written by the indexing model from the issue text.