docs: Improve content in /ai/agent-panel and /ai/rules (#42055)

- Clarify about first-party supported features in external agents
- Create new section for selection as context for higher visibility
- Add keybindings for agent profiles
- Fix outdated setting using `assistant` instead of `agent`
- Add keybinding for accessing the rules library

Release Notes:

- N/A

docs/src/ai/rules.md

@@ -1,7 +1,7 @@
 # Using Rules {#using-rules}
 
 A rule is essentially a prompt that is inserted at the beginning of each interaction with the Agent.
-Currently, Zed supports `.rules` files at the directory's root and the Rules Library, which allows you to store multiple rules for on-demand usage.
+Currently, Zed supports adding rules through files inserted directly in the worktree or through the Rules Library, which allows you to store multiple rules for constant or on-demand usage.
 
 ## `.rules` files
 
@@ -30,7 +30,7 @@ You can use the inline assistant right in the rules editor, allowing you to auto
 2. Click on the Agent menu (`...`) in the top right corner.
 3. Select `Rules...` from the dropdown.
 
-You can also use the `agent: open rules library` command while in the Agent Panel.
+You can also reach it by running {#action agent::OpenRulesLibrary} in the command palette or through the {#kb agent::OpenRulesLibrary} keybinding.
 
 ### Managing Rules