Add MCPB packaging and Claude Code plugin for pdf-server (#491)

* Add MCPB packaging and Claude Code plugin for pdf-server

Two distribution paths for the pdf-server:

1. **MCPB bundle** (Claude Desktop MCP Directory):
   - manifest.json: v0.3 manifest with tools, compatibility, privacy
   - .mcpbignore: excludes source/tests from bundle
   - icon.png: 64x64 PDF document icon

2. **Claude Code plugin** (plugin/):
   - .mcp.json: declares local stdio server via npx
   - commands: /pdf-research:read, /pdf-research:summarize
   - skills: pdf-reading skill for document navigation
   - Tested end-to-end: MCP server connects, all tools available

The plugin uses a local stdio MCP server pattern — the first known
instance in a knowledge-work plugin (all existing plugins use remote
HTTP connectors).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* Run prettier:fix to satisfy CI formatting checks

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

examples/pdf-server/plugin/README.md

@@ -0,0 +1,40 @@
+# PDF Research Plugin
+
+Read and analyze PDF documents using a local MCP server. Designed for
+academic paper review, document analysis, and research workflows.
+
+## What It Does
+
+- **Open PDFs** from local files, arXiv, bioRxiv, and other academic sources
+- **Interactive viewer** with search, navigation, and zoom
+- **AI-powered analysis** -- summarize, extract key points, compare papers
+
+## Commands
+
+| Command                   | What it does           |
+| ------------------------- | ---------------------- |
+| `/pdf-research:read`      | Open a PDF for reading |
+| `/pdf-research:summarize` | Summarize a document   |
+
+## How It Works
+
+This plugin uses a **local MCP server** (`@modelcontextprotocol/server-pdf`)
+that runs on your machine via `npx`. No API keys or remote services needed --
+the PDF server starts automatically when the plugin loads.
+
+This is different from other knowledge-work plugins which use remote HTTP
+connectors. The local server pattern enables offline PDF access and avoids
+the need for a remote deployment.
+
+## Requirements
+
+- Node.js >= 18
+- Internet for remote PDFs (arXiv, etc.)
+
+## Supported PDF Sources
+
+- Local files (file paths in your working directory)
+- [arXiv](https://arxiv.org) papers
+- [bioRxiv](https://biorxiv.org) / [medRxiv](https://medrxiv.org) preprints
+- [chemRxiv](https://chemrxiv.org), [Zenodo](https://zenodo.org), [OSF](https://osf.io)
+- [HAL Science](https://hal.science), [SSRN](https://ssrn.com)