Add load: on-demand flag to SKILL.md frontmatter to prevent auto-loading in context

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

All skills in .claude/skills/<name>/SKILL.md are auto-loaded into the context window at
session start. Users with multiple skills only need a subset loaded automatically —
others should only be invoked when explicitly called, but there's no way to opt out. This
creates unnecessary context bloat, especially as the skills list grows.

Proposed Solution

Add an optional load frontmatter flag to SKILL.md:

• load: auto (default) — loads at session start as today
• load: on-demand — only loads when /skill-name is explicitly invoked

Alternative Solutions

_No response_

Priority

Medium - Would be very helpful

Feature Category

CLI commands and flags

Use Case Example

_No response_

Additional Context

_No response_