Add comprehensive DXT compliance with tool schemas and metadata validation

[Copilot]

This PR implements complete DXT (Desktop Extension) compliance for the Raindrop MCP server by adding comprehensive tool metadata, schemas, and validation as required by the DXT MANIFEST.md specification.

Changes Made

📋 Enhanced Manifest.json

• Added 25 tools with complete metadata including stable IDs, descriptions, categories, and schemas
• Organized tools into 7 categories: Collections (7), Bookmarks (6), Tags (2), Highlights (4), User (2), Import/Export (3), General (1)
• Added comprehensive schemas: inputSchema and outputSchema for all tools following JSON Schema format
• Enhanced description: Detailed overview of Raindrop.io MCP capabilities
• Added compatibility section: Cross-platform support (darwin/win32/linux) with Node.js >=16.0.0
• Improved user configuration: Better API key guidance with direct link to settings
• Set tools_generated: true: Indicates dynamic tool generation at runtime

🧪 Validation & Testing

• New test suite: tests/manifest.test.ts with 9 comprehensive test cases
• 441 assertions validating all aspects of DXT compliance
• 100% pass rate ensuring manifest correctness

🔧 Tool Documentation Examples

Each tool now includes complete metadata:

{
  "id": "bookmark_search",
  "name": "bookmark_search", 
  "description": "Search bookmarks with advanced filtering. This is the primary tool for finding bookmarks. Supports full-text search, tag filtering, date ranges, and collection scoping.",
  "category": "Bookmarks",
  "inputSchema": {
    "type": "object",
    "properties": {
      "search": { "type": "string", "description": "Search query" },
      "collection": { "type": "number", "description": "Collection ID" },
      "tags": { "type": "array", "items": { "type": "string" }, "description": "Filter by tags" }
    }
  },
  "outputSchema": { /* MCP content format */ }
}

Validation Results

✅ All required DXT fields present and properly formatted
✅ 25 tools documented with unique, stable IDs and clear descriptions
✅ Complete schema definitions for input validation and output formatting
✅ Category organization following logical functional groupings
✅ Platform compatibility specified for broad deployment support
✅ Test coverage ensuring ongoing compliance validation

Benefits

• DXT Ecosystem Ready: Full compliance with Desktop Extension specifications
• Enhanced Discoverability: Clear tool descriptions and categorization for AI systems
• Robust Validation: Comprehensive input/output schemas prevent runtime errors
• Maintainable Structure: Organized categories and consistent naming conventions
• Future-Proof: Ready for extension marketplace deployment and third-party integrations

The Raindrop MCP server now provides a fully compliant DXT extension with 25 well-documented tools for comprehensive bookmark management, making it ready for production deployment in Claude Desktop and other MCP-compatible environments.

Fixes #8.

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