fix(adapters): conform to standard tool structure

[olimorris]

Description

In the past year, adapters such as Gemini and OpenAI Responses have embedded reasoning and thought signatures in their tool call requests. These are, of course, unique to them. This now means that if a user starts a chat with Gemini and executes a tool call, and attempts to move the chat over to OpenAI Responses, then they'd receive an error back from the server.

This PR does two things:

1. Firstly, it ensures that the tool structure on the chat messages is consistent across all adapters
2. It prevents users from switching adapters after a tool call or reasoning has taken place.

I plan on adding a /fork slash command to allow users to create a duplicate of the current chat, prior to any tool calling.

AI Usage

Opus 4.6

Related Issue(s)

Screenshots

Checklist

• I've read the contributing guidelines and have adhered to them in this PR
• I confirm that this PR has been majority created by me, and not AI (unless stated in the "AI Usage" section above)
• I've run make all to ensure docs are generated, tests pass and StyLua has formatted the code
• (optional) I've added test coverage for this fix/feature
• (optional) I've updated the README and/or relevant docs pages