Improve tool activation UX

[nsarrazin]

Currently, you can activate a tool from the /tools page while not using a tool calling model. This leads to confusing behaviour where you click "activate", go to a new chat and expect the tool to be used.

Two options:

1. Disable the "activate" button if the currently active model is not a tool model, with a helper text/tooltip to let the user know to activate a model with tool calling in order to use tools.

2. Let the user activate the tool but show a helper in the tool modal that lets them know that tools won't be active until they use a compatible model. (might be easier to miss)