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/SUMMARY.md

@@ -45,13 +45,14 @@
 - [Overview](./ai/overview.md)
 - [Agent Panel](./ai/agent-panel.md)
   - [Tools](./ai/tools.md)
-  - [Model Temperature](./ai/temperature.md)
 - [Inline Assistant](./ai/inline-assistant.md)
 - [Edit Prediction](./ai/edit-prediction.md)
 - [Text Threads](./ai/text-threads.md)
 - [Rules](./ai/rules.md)
 - [Model Context Protocol](./ai/mcp.md)
 - [Configuration](./ai/configuration.md)
+  - [LLM Providers](./ai/llm-providers.md)
+  - [Agent Settings](./ai/agent-settings.md)
 - [Subscription](./ai/subscription.md)
   - [Plans and Usage](./ai/plans-and-usage.md)
   - [Billing](./ai/billing.md)