docs: update 12-7-ai-conversational-assistant.md

[habib424]

Drafted by Ship Ship 🚢 — confidence 🟢 high

What changed

Added a new "Skills" subsection under "Using LCI in the Web App" explaining: (1) what skills are (user-created shortcuts for common prompts), (2) how to trigger them via typing '/' or clicking the "Run skill" button, (3) the interactive empty-state prompt for users with no skills that offers an example, and (4) how filtering works as you type.

Source PRs

• axolotl#3996 — feat(LCI): improve skills menu UX with run button and empty state

How to use this PR

1. Review the diff against the existing article — focus on accuracy and customer voice.
2. Merge if it reads well. Edit and push to this branch if it needs adjustment.
3. Close without merging if the article doesn't actually need this update.

Once we have a track record of clean drafts, we'll graduate to auto-merge with a delay buffer. For now: human-in-the-loop.