settings_ui: Move skills management into settings UI (#58701)

Closes AI-344
Closes AI-342

Moves agent skills management out of the agent panel and into the
settings UI. The skill creator (previously its own crate) now lives in
`settings_ui` as a settings page, alongside the skills setup page. The
agent panel's ellipsis menu now links to the settings page instead of
hosting skill management directly.

Release Notes:

- Improved agent skills management by moving it into the settings UI

---------

Co-authored-by: Danilo Leal <daniloleal09@gmail.com>

docs/.doc-examples/complex-feature.md

@@ -242,10 +242,17 @@ See [Feature-specific models](./ai/agent-settings.md#feature-specific-models) fo
 }
 ```
 
-To customize the format of generated commit messages, run {#action agent::OpenRulesLibrary} and select the "Commit message" rule on the left side.
-From there, you can modify the prompt to match your desired format.
+To add custom instructions that apply only to commit message generation, use the `commit_message_instructions` field in your agent settings:
 
-Any specific instructions for commit messages added to [Rules files](./ai/rules.md) are also picked up by the model tasked with writing your commit message.
+```json [settings]
+{
+  "agent": {
+    "commit_message_instructions": "Use the Conventional Commits format: <type>(<scope>): <description>."
+  }
+}
+```
+
+These instructions are sent to the model in addition to any instruction files, such as `.rules` or `AGENTS.md`. To add instructions that apply to both commit messages and the agent more broadly, use the global `AGENTS.md` file located `~/.config/zed/AGENTS.md` on macOS and Linux, `%APPDATA%\Zed\AGENTS.md` on Windows.
 
 ## Git Integrations {#git-integrations}