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/.claude-plugin/plugin.json

@@ -0,0 +1,8 @@
+{
+  "name": "pdf-research",
+  "version": "0.1.0",
+  "description": "Read, navigate, and analyze PDF documents — academic papers, reports, and local files. Uses a local PDF MCP server for interactive viewing and text extraction.",
+  "author": {
+    "name": "Anthropic"
+  }
+}