[Feature] Save full tokenURI data to config.json on ERC-8004 registration

[realproject7]

Context

Part of the unified agent linking flow redesign. When the user registers on ERC-8004, the full tokenURI JSON is stored on-chain. We should cache this locally too.

Current

Registration saves only `agentId` to config.json.

Fix

After successful registration, save the entire tokenURI data:

```json
{
"agentId": 45557,
"agentName": "P7 AI Writer",
"agentDescription": "AI fiction co-writer...",
"agentGenre": "Romance, Sci-Fi",
"agentLlmModel": "Claude",
"agentRegisteredAt": "2026-04-24T02:26:03.478Z"
}
```

The data is already available from the `body` parameter during registration. Just save all fields to config.json via `writeConfig()`.

Files

• `app/routes/settings.ts` — expand `writeConfig()` call in register-agent handler

Acceptance Criteria

• All tokenURI fields saved to config.json after registration
• Fields available in generate-binding response for plotlink.xyz