docs: Overhaul AI documentation (#29747)

To support the Agentic Editing launch. To dos before merging:

- [ ] Anything marked as `todo!` within `docs/src` (Anyone)
- [x] Check all internal links (Joe)
- Joe: I checked all links and fixed all aside from a few that I
annotated with `todo!` comments
- [ ] Update images (Danilo)
- [ ] Go over / show images of tool cards in agent panel overview
(Danilo)
- [ ] Point billing FAQ to new billing docs (Joe)
- [x] Redirects external links
    - [ ] Needs testing
- [x] Delete old docs
- [ ] Ensure all mentioned bindings use the `{#kb ...}` format and that
they are rendering correctly
- [ ] All agent-related actions are now `agent::` and not `assistant::`
- [x] Mention support of `.rules` files in `rules.md`

Release Notes:

- N/A

---------

Co-authored-by: Joseph T. Lyons <josephtlyons@gmail.com>
Co-authored-by: morgankrey <morgankrey@gmail.com>
Co-authored-by: Smit Barmase <37347831+smitbarmase@users.noreply.github.com>
Co-authored-by: Ben Kunkle <Ben.kunkle@gmail.com>
Co-authored-by: Peter Tripp <peter@zed.dev>
Co-authored-by: Ben Kunkle <ben@zed.dev>
Co-authored-by: Mikayla Maki <mikayla.c.maki@gmail.com>
Co-authored-by: Ben Brandt <benjamin.j.brandt@gmail.com>

docs/src/SUMMARY.md

@@ -37,18 +37,24 @@
 - [Environment Variables](./environment.md)
 - [REPL](./repl.md)
 
-# Assistant
+# AI
 
-- [Overview](./assistant/assistant.md)
-- [Configuration](./assistant/configuration.md)
-- [Assistant Panel](./assistant/assistant-panel.md)
-- [Contexts](./assistant/contexts.md)
-- [Inline Assistant](./assistant/inline-assistant.md)
-- [Commands](./assistant/commands.md)
-- [Prompts](./assistant/prompting.md)
-- [Context Servers](./assistant/context-servers.md)
-  - [Model Context Protocol](./assistant/model-context-protocol.md)
-- [Model Improvement](./model-improvement.md)
+- [Overview](./ai/ai.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)
+- [Subscription](./ai/subscription.md)
+  - [Plans and Usage](./ai/plans-and-usage.md)
+  - [Billing](./ai/billing.md)
+  - [Models](./ai/models.md)
+- [Use Your Own API Keys](./ai/custom-api-keys.md)
+- [Privacy and Security](./ai/privacy-and-security.md)
+  - [AI Improvement](./ai/ai-improvement.md)
 
 # Extensions