document-skills and example-skills plugins install identical content, causing duplicate skills

## Description

When installing both `document-skills` and `example-skills` plugins from `anthropic-agent-skills`, they contain **identical skills**, causing duplicates in Claude Code's context window.

## Expected Behavior

According to the repo README:
- `document-skills` should contain only the production document skills (docx, pdf, pptx, xlsx)
- `example-skills` should contain the open-source educational examples (algorithmic-art, canvas-design, etc.)

## Actual Behavior

Both plugins install **all 17 skills** from the `skills/` directory:

```
=== document-skills ===
algorithmic-art, brand-guidelines, canvas-design, doc-coauthoring, docx,
frontend-design, internal-comms, mcp-builder, pdf, pptx, skill-creator,
slack-gif-creator, theme-factory, web-artifacts-builder, webapp-testing, xlsx

=== example-skills ===
(identical list)
```

Both use the same commit hash in the cache (`69c0b1a06741`).

## Impact

- **~50k wasted tokens** on duplicate skill definitions
- Skills like `pptx` (6.3k tokens) appear twice in `/context`
- Reduces available context for actual work

## Steps to Reproduce

1. Install Claude Code
2. Run: `claude plugin install document-skills@anthropic-agent-skills`
3. Run: `claude plugin install example-skills@anthropic-agent-skills`
4. Run `/context` in Claude Code
5. Observe duplicate skills in the "Plugin" section

## Environment

- Claude Code **v2.0.76**
- macOS 15.6.1
- Both plugins installed at user scope

## Suggested Fix

The plugin packaging should respect the intended separation, or the marketplace should only expose one unified plugin that contains all skills without duplication.

## Workaround

Uninstall one of the duplicate plugins:
```bash
claude plugin uninstall example-skills@anthropic-agent-skills
```