Add Streamable HTTP transport to MCPToolProvider (TypeScript + Python)

[cornelcroi]

Problem

MCPToolProvider in both trees supports only stdio and sse transports. HTTP+SSE is the legacy transport, deprecated in the MCP spec since 2025-03-26. Streamable HTTP is the current standard HTTP transport, and everything in the new 2026-07-28 spec revision (stateless core, routing headers, caching) lands on it. Today we cannot connect to a Streamable HTTP MCP server at all — our own examples/mcp-shop-server speaks it and can only be consumed from Swift.

Proposal

Add a new accepted value "streamable-http" for MCPServerConfig.type, reusing the existing url and headers fields. No new fields, no changes to "stdio" / "sse".

• TypeScript: lazy-import StreamableHTTPClientTransport from @modelcontextprotocol/sdk/client/streamableHttp.js — already available in the v1 SDK we target.
• Python: lazy-import streamablehttp_client from mcp.client.streamable_http — already available in mcp 1.x.
• Tests mirroring the existing SSE transport tests in both trees.
• Docs: add the transport to the mcp-tool-provider page (TS + Python examples), note that SSE remains supported for legacy servers.

Fully additive: existing configurations behave exactly as before.

Prerequisite for 2026-07-28 protocol support (separate issues).