docs: fix broken MCP SDKs link in host-integration.md - #3598

The previous link pointed to a 404 page.
Updated to the current SDKs documentation page.

Fixes #3589

Summary

Why

Fixes #

What changed

MCP impact

• No tool or API changes
• Tool schema or behavior changed
• New tool added

Prompts tested (tool changes only)

Security / limits

• No security or limits impact
• Auth / permissions considered
• Data exposure, filtering, or token/size limits considered

Tool renaming

• I am renaming tools as part of this PR (e.g. a part of a consolidation effort)
  • I have added the new tool aliases in deprecated_tool_aliases.go
• I am not renaming tools as part of this PR

Note: if you're renaming tools, you must add the tool aliases. For more information on how to do so, please refer to the official docs.

Lint & tests

• Linted locally with ./script/lint
• Tested locally with ./script/test

Docs

• Not needed
• Updated (README / docs / examples)

Summary

Fixes the broken "MCP SDKs" link in docs/host-integration.md.

The previous URL (https://modelcontextprotocol.io/sdk/java/mcp-overview) returned 404.
Updated it to the current official SDKs page: https://modelcontextprotocol.io/docs/sdk

Fixes #3589