Incorrect URL in mcpSse Client

[e5l]

Summary:
Client requests .../sse//message?sessionId=... instead of .../message?sessionId=..., causing 404 errors.

Steps to Reproduce

// Server (works)
embeddedServer(CIO, host = "0.0.0.0", port = port) {
    MCP { configureServer() }
}.start(wait = true)

// Client (broken)
val client = HttpClient(CIO) {
    install(SSE)
}.mcpSse("http://localhost:$port/sse")

Issue

Trailing slash in the base URL causes double slashes in the request path.

Impact

Breaks client-server communication unless manually corrected.