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/CONNECTORS.md

@@ -0,0 +1,16 @@
+# Connectors
+
+## Local MCP Server
+
+This plugin uses a **local MCP server** instead of a remote connector.
+The PDF server runs on your machine via `npx`.
+
+| Category   | Server                             | How it runs                            |
+| ---------- | ---------------------------------- | -------------------------------------- |
+| PDF viewer | `@modelcontextprotocol/server-pdf` | Local stdio via `npx` (auto-installed) |
+
+### Requirements
+
+- Node.js >= 18
+- Internet access for remote PDFs (arXiv, bioRxiv, etc.)
+- No API keys or authentication needed