FF Expert context awareness of Node-RED instance state

**Parent Deliverable:** FlowFuse/product#47 — Expert as Agentic Co-pilot

## Problem
FF Expert currently provides AI suggestions without understanding what already exists in a Node-RED instance. This limits the relevance and usefulness of generated recommendations.

An example of this: The expert suggesting users install packages they already have, or providing generic advice that doesn't account for their existing setup.

### Opportunity ahead

This builds towards the opportunity of the FlowFuse expert being able to adjust existing things/workflows/settings inside of Node-RED.

## Proposed Solution

Extend the NR Assistant communication framework (established in #6497) to support contextual queries. These capabilities are all achievable by following the existing messaging patterns established in #6497.

### Initial Focus: Installed Packages (2.27)

**Scope**: Node-RED immersive editor experience

The first iteration will focus on making the expert aware of installed packages. This allows the expert to:
- Say "using package X that you already have installed" instead of suggesting reinstallation
- Demonstrate context awareness without requiring users to explain their setup
- Establish the messaging pattern for future context queries

**Sub-issues**:
- #6535 Assistant: Expose installed package list
- #6536 Expert: Consume and utilize package information in responses
- #6537 (Stretch) Streamline package installation UX

### Future Iterations

Once the pattern is established, expand to include:
- Summary of nodes in use across flows
- Basic flow structure information
- Selected nodes in editor
- Editor state (to prevent invalid operations)

**Note**: Future expansions require clear user stories defining what questions users want answered and what tasks they want to accomplish.

## Dependencies
- #6497 (NR Assistant ↔ FF Expert communication)