FlowFuse Expert should proactively recommend nr-assistant plugin upgrades

**Parent Deliverable:** FlowFuse/product#48 — Expert Discovery and Default Enablement

## Problem

Users running outdated versions of `@flowfuse/nr-assistant` are missing newer features without realizing it. Current upgrade notifications only appear in:

• Node-RED Palette Manager (requires user to manually check)
• Instance overview (only for stack upgrades)

This creates friction because users don't know they're missing capabilities. In a real example, a user on v0.6.0 couldn't get example flows because that feature requires v0.8.0 — but there was no indication of why the feature wasn't working.

## Proposed Solution

Display a contextual banner in the FlowFuse Expert chat interface when the user's nr-assistant version is outdated, suggesting they upgrade to access the latest features.

**Example copy**: "To get the most from the Expert, upgrade your Node-RED plugins to latest"

## Technical Context

• The Expert already has access to the installed nr-assistant version (added with foresight)
• Version info is available in the Vuex store
• This should be a relatively low-effort change with high impact on feature discoverability

## Acceptance Criteria

- [ ] Expert detects when nr-assistant is below latest version
- [ ] Banner/notification appears in Expert UI recommending upgrade
- [ ] Link or instructions to upgrade are provided

## Context

Slack thread: https://flowfuse.slack.com/archives/C09QS57R8AD/p1768828470387759