feat: Add tool annotations for improved LLM tool understanding

[bryankthompson]

Summary

Adds MCP tool annotations (readOnlyHint, openWorldHint) to all 10 tools to help LLMs better understand tool behavior and make safer decisions about tool execution.

Changes

• Bump @modelcontextprotocol/sdk from 1.0.1 to ^1.7.0 for annotation support
• Bump zod from ^3.24.1 to ^3.25.0 for SDK compatibility
• Added readOnlyHint: true to all 10 tools (pure converters, no side effects)
• Added openWorldHint: true to URL-based tools that fetch external content:
  • youtube-to-markdown
  • bing-search-to-markdown
  • webpage-to-markdown
• Added title annotations for human-readable display

Why This Matters

• Annotations provide semantic metadata that helps LLMs understand tool behavior
• LLMs can make better decisions about when to use tools and in what order
• readOnlyHint: true enables MCP clients to auto-approve safe operations
• openWorldHint: true signals tools that access external resources

Testing

• pnpm run build succeeds
• Live verification: Started server and confirmed tools/list returns annotations
• All 10 tools have correct annotations

Before/After

Before:

{
  "name": "youtube-to-markdown",
  "description": "Convert a YouTube video to markdown..."
}

After:

{
  "name": "youtube-to-markdown",
  "description": "Convert a YouTube video to markdown...",
  "annotations": {
    "title": "YouTube to Markdown",
    "readOnlyHint": true,
    "openWorldHint": true
  }
}