Add command wrapper skills

[Avg8888]

What Problem This Solves

Some harnesses can install and expose skills but do not have a prompt/slash-command primitive. The bundled visual-explainer workflows currently live primarily as command templates, which makes /diff-review, /plan-review, /generate-web-diagram, and the other shortcuts less portable outside command-aware harnesses.

AI-assisted PR.

Why This Change Was Made

This adds user-invoked skill wrappers for each bundled command workflow:

• diff-review
• fact-check
• generate-slides
• generate-visual-plan
• generate-web-diagram
• plan-review
• project-recap

Each wrapper loads the main visual-explainer skill, preserves the existing workflow instructions, and sets disable-model-invocation: true so the workflows are available on demand without expanding the model's automatic skill list. The package metadata, Claude plugin manifest, legacy Pi installer, and harness docs now advertise the command wrapper skills alongside the existing prompt templates.

User Impact

Users on skill-only harnesses can invoke the same workflows as skills instead of manually finding command markdown. Existing command-template installs remain documented for harnesses that support prompts/slash commands.

Evidence

• Verified all generated wrapper skills include required frontmatter (name, description, disable-model-invocation: true, user-invocable: true) and reference the main skill.
• Verified command template frontmatter includes disable-model-invocation: true.
• Validated JSON manifests with python3 -m json.tool package.json and python3 -m json.tool plugins/visual-explainer/.claude-plugin/plugin.json.
• Smoke-tested install-pi.sh with a temporary HOME, confirming it installs the main skill, a command wrapper skill, and a prompt template.

[Avg8888]

Closing this PR in favor of a feature request issue.