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/book.toml

@@ -25,6 +25,17 @@ enable = false
 "/assistant.html" = "/docs/assistant/assistant.html"
 "/developing-zed.html" = "/docs/development.html"
 "/conversations.html" = "/community-links"
+"/assistant/assistant.html" = "/ai/ai.html"
+"/assistant/configuration.html" = "/ai/configuration.html"
+"/assistant/assistant-panel.html" = "/ai/agent-panel.html"
+"/assistant/contexts.html" = "/ai/text-threads.html"
+"/assistant/inline-assistant.html" = "/ai/inline-assistant.html"
+"/assistant/commands.html" = "/ai/text-threads.html"
+"/assistant/prompting.html" = "/ai/rules.html"
+"/assistant/context-servers.html" = "/ai/mcp.html"
+"/assistant/model-context-protocol.html" = "/ai/mcp.html"
+"/model-improvement.html" = "/ai/ai-improvement.html"
+
 
 # Our custom preprocessor for expanding commands like `{#kb action::ActionName}`,
 # and other docs-related functions.