Load and apply a skill by name. Usage: /skill <name> or /skill (to list all available skills).

If $ARGUMENTS is empty, scan these directories for SKILL.md files and list all available skills:
- .claude/skills/
- frontend/.claude/skills/
- backend/.claude/skills/

Format the list as a table with columns: Name, Location, Description (first line of the SKILL.md after the frontmatter).

If $ARGUMENTS contains a skill name:
1. Search for the skill in all three directories above
2. Read the SKILL.md file completely
3. Apply its instructions to the current conversation context
4. Confirm with: "Skill **<name>** loaded from <location>."

If the skill is not found, show the available skills list with a message "Skill '<name>' not found."
