assistant2: Allow creating agent profiles via settings (#27216)

This PR adds support for creating new agent profiles via the settings:

```json
{
  "assistant": {
    "profiles": {
      "lua": {
        "name": "Lua",
        "tools": {
          "lua-interpreter": true
        }
      },
      "lua-thinking": {
        "name": "Lua + Thinking",
        "tools": {
          "lua-interpreter": true,
          "thinking": true
        }
      }
    }
  }
}
```

Release Notes:

- N/A

crates/assistant2/src/assistant.rs

@@ -1,5 +1,4 @@
 mod active_thread;
-mod agent_profile;
 mod assistant_configuration;
 mod assistant_model_selector;
 mod assistant_panel;