docs: Restructure and improve AI configuration docs (#35133)

Adding a number of settings that weren't documented, restructuring
things a bit to separate what is model-related settings from agent panel
usage-related settings, adding the recently introduced `disable_ai` key,
and more.

Release Notes:

- Improved docs around configuring and using AI in Zed

docs/src/ai/agent-panel.md

@@ -8,7 +8,7 @@ If you're using the Agent Panel for the first time, you need to have at least on
 You can do that by:
 
 1. [subscribing to our Pro plan](https://zed.dev/pricing), so you have access to our hosted models
-2. or by [bringing your own API keys](./configuration.md#use-your-own-keys) for your desired provider
+2. or by [bringing your own API keys](./llm-providers.md#use-your-own-keys) for your desired provider
 
 ## Overview {#overview}
 
@@ -87,7 +87,7 @@ You can also do this at any time with an ongoing thread via the "Agent Options"
 
 ## Changing Models {#changing-models}
 
-After you've configured your LLM providers—either via [a custom API key](./configuration.md#use-your-own-keys) or through [Zed's hosted models](./models.md)—you can switch between them by clicking on the model selector on the message editor or by using the {#kb agent::ToggleModelSelector} keybinding.
+After you've configured your LLM providers—either via [a custom API key](./llm-providers.md#use-your-own-keys) or through [Zed's hosted models](./models.md)—you can switch between them by clicking on the model selector on the message editor or by using the {#kb agent::ToggleModelSelector} keybinding.
 
 ## Using Tools {#using-tools}