Improve Error Reporting When Desktop Agent *adaptor* Iframe doesn't load

## Minor Issue

Poor error reporting after the initial hello:

```
FDC3 getAgent: Sending hello message to communication iframe
index-DnkoWixp.js:76 FDC3 getAgent: HelloHandler: Sending hello msg:
{
"type": "WCP1Hello",
"meta": {
"connectionAttemptUuid": "126e53f9-3a60-4ded-9580-683f440f0de2",
"timestamp": "2026-01-19T13:34:24.876Z"
},
"payload": {
"channelSelector": true,
"fdc3Version": "2.2",
"resolver": true,
"identityUrl": "https://fdc3.finos.org/toolbox/fdc3-workbench/",
"actualUrl": "https://fdc3.finos.org/toolbox/fdc3-workbench/"
}
}
index-DnkoWixp.js:76 FDC3 getAgent: DesktopAgentPreloadLoader.get(): timeout (1000 ms) at 2026-01-19T13:34:25.845Z
index-DnkoWixp.js:76 FDC3 getAgent: DesktopAgentPreloadLoader: Cleaning up
index-DnkoWixp.js:76 FDC3 getAgent: PostMessageLoader.get(): timeout (1000 ms) at 2026-01-19T13:34:25.845Z
index-DnkoWixp.js:76 FDC3 getAgent: PostMessageLoader: Cleaning up
index-DnkoWixp.js:76 FDC3 getAgent: Discovery results: [
{
"status": "rejected",
"reason": "AgentNotFound"
},
{
"status": "rejected",
"reason": "AgentNotFound"
}
]
```

### Area of Issue

- [ ] App Directory
- [x] API
- [ ] Context Data
- [ ] Intents
- [ ] Desktop Agent Bridging
- [ ] Use Cases
- [x] Other. get-agent

### Issue Description

When connecting to a desktop agent, sometimes CORS can get in the way. For example, this happens when I run Sail on localhost. It tries to load an iframe called embed.html. However, if this fails to load, nothing really shows up in the log.

After digging around, I discovered the error on the network panel, but this isn't ideal:

### Additional Context