Allow skills to be hot-reloaded without restarting the session

Currently, skills installed to ~/.claude/skills/ during a running session aren't picked up until a full restart. This means any time you install, update, or symlink a new skill mid-session, you have to kill and reopen Claude Code to use it — even though the files are already on disk.

Request: Add a command (e.g. /reload-skills or /rescan-skills) that re-scans the skills directory and makes newly installed skills available in the current session without a restart.

Why it matters:

• Skills installed via install.sh scripts (e.g. from a git clone) are a common pattern. The install-then-restart friction is jarring, especially when onboarding someone.
• Iterating on a skill you're authoring requires a session bounce after every change, which slows down the feedback loop significantly.

Workaround today: restart the session.