FF Cross-Instance Shared Libraries

### Description

We’d like FlowFuse instances to be able to share libraries with each other.

Use case
• Enterprise/Cloud FlowFuse:
• Where dev happens, reviews, and shared libraries are maintained.
• May host a few enterprise-level runtimes.
• Site FlowFuse servers (on-prem, OT side):
• Manage local Node-RED runtimes talking to PLCs.
• Need to stay autonomous if WAN/cloud is down.

Right now, each site has to manually export/import flows from the “enterprise” instance. That leads to drift and lots of copy-paste.

What we want
• Mark one FF instance (or FF Cloud project) as a library provider.
• Other FF instances (site servers) can be configured as library consumers:
• See the shared library in their Library UI as read-only.
• Pull/import flows, subflows, and shared code from the enterprise library into local projects.
• Optionally pull updates when new versions are published.

Why this matters
• Single, managed code base for all sites.
• Sites stay fully autonomous for OT operations.
• Cloud dev workflow still works: build in FF Cloud, then sync the same library to on-prem FF instances at each site.

TL;DR
Let one FlowFuse instance expose its flow/library assets to another FlowFuse instance, so an enterprise FF (or FF Cloud) can be the central code library while site FF servers stay autonomous on-prem.

### Which customers would this be available to

Enterprise

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

I can not provide an initial effort estimate