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/commands/read.md

@@ -0,0 +1,21 @@
+---
+description: Open a PDF for reading and analysis
+---
+
+# Read PDF
+
+Open a PDF document for interactive reading. Accepts local file paths,
+arXiv URLs, or other academic paper URLs.
+
+## Instructions
+
+1. If the user provides a URL or file path, call `display_pdf` with that URL
+2. If no URL given, call `list_pdfs` first to show available documents
+3. After displaying, offer to summarize, extract key points, or answer questions
+
+## Supported Sources
+
+- Local files (drag-and-drop or file path)
+- arXiv papers (arxiv.org/abs/... or arxiv.org/pdf/...)
+- bioRxiv, medRxiv, chemRxiv preprints
+- Zenodo, OSF, HAL, SSRN