docs: Document how to open the Skill Creator (#57314)

Documents the ways to open the Skill Creator in `docs/src/ai/skills.md`:

- From the Agent Panel using the keybinding ({#kb
agent::OpenRulesLibrary})
- From the Agent Panel `...` menu > **Skills**
- From the command palette via {#action agent::OpenSkillCreator}

Release Notes:

- N/A
2b506483b2María Craig committed on 5/20/2026, 8:42:25 PM· committed by GitHubparentc7b9039
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