Allow projects to force-load skills automatically

Problem

Skills can be configured with a description field that hints when they should auto-activate, but there's no way to guarantee a skill is always loaded in a given project. The only options today are:

1. The user manually invokes the skill (/skill-name)
2. Claude decides to invoke it based on the description match
3. CLAUDE.md instructions ask Claude to invoke it (still relies on Claude following through)

None of these are enforced.

Proposed Solution

Add a project-level configuration (e.g., in .claude/settings.local.json or CLAUDE.md frontmatter) that always preloads specified skills into the session context:

{
  "skills": {
    "always_load": ["manimce-best-practices"]
  }
}

When a skill is in always_load, its content would be injected into every session in that project directory automatically — no invocation needed.

Use Case

I'm working on a Manim animation project with a manimce-best-practices skill installed. I want every Claude session in this project to have those best practices loaded, without having to remember to invoke the skill or rely on auto-detection.