docs: clarify inline metadata-only skill scope

[ketpatil77]

Summary

• clarify in skills guide that inline { name, description } entries are catalog-only
• clarify in API reference that inline metadata does not load SKILL.md or supporting files
• direct users toward imported or workspace-discovered skills for real reusable behavior

Testing

• Docs-only change
• Verification: inspected rendered markdown diff for apps/docs/src/content/docs/guide/skills.md and apps/docs/src/content/docs/api/agent-api.md
• Note: local pnpm exec prettier --check ... could not run here because prettier binary was not available in this worktree

Closes #433

[astrobot-houston]

Thanks for the contribution! We're closing this PR and moving the conversation to the issue: #436

We've moved to a model where bugs and feature proposals are discussed in issues/discussions before code review, so the community can help prioritize and shape the work. Your branch is linked from the new thread so the implementation isn't lost — please join us there to continue the conversation.

— astrobot 🤖