Agents should auto-install FlowFuse and certified nodes instead of asking the user

[cstns]

Current behaviour

When an agent, whether the first party Expert or a third party agent over MCP, builds a flow that needs a node that isn't installed, it opens the editor's palette manager with the package pre-selected and the user confirms the install. This is by design, a deliberate security decision: agents don't get to put arbitrary code into a runtime, the user always has the final say.

The same applies at instance creation. platform_create_hosted_instance takes no module list, so even when the agent already knows the flow it is about to build needs certain nodes, it can't provision them up front.

What we want

FlowFuse scoped plugins and certified nodes are vetted by us, so for those specific packages the security concern doesn't apply and we can skip the confirmation. Concretely, while a first or third party agent is driving the automation:

1. When the agent creates an instance and knows it will need certain nodes later, those nodes should be preinstalled as part of creation. This also sidesteps the fact that installing into a running instance can require a restart depending on the package.
2. When the agent needs one of these nodes on an existing instance while building a flow, it should install it automatically instead of sending the user to the palette manager.

Anything outside those two scopes keeps the current confirmation behaviour, and the manual (non-agent) flow doesn't change.

[knolleary]

One note - not all instances will have equal access to certified nodes. For example, a Hub customer doesn't have OPC-UA - but if they ask the agent to create an opc-ua flow for them, we need to handle that appropriately. Essentially, the agent will need to know what nodes are available out of the FF owned ones.

[andypalmi]

@knolleary The process to enroll customer to certified nodes is the following, right?

[knolleary]

@andypalmi yes.