Log HTTP request bodies and tool responses at debug level

[aragossa]

In HTTP mode, handleMCPHTTP logs every request body and every response at info, the default log level:

• Request body: ... contains the tool arguments the agent passes (e-mail addresses, keys, anything a tool takes as a parameter).
• Response: ... contains the tool output, i.e. whatever the shell command printed (kubectl/aws output, file contents, environment values).

With --logfile these lines also go to the file. The stdio mode does not log them.

This change moves those three lines to debug, so --log-level debug still shows them for troubleshooting, while the default info level keeps only the connection line and method=... id=....

Tested locally: built from main, ran mcp --http with a one-tool config, sent initialize and tools/call with curl. Before: arguments and output in the log at info. After: only the connection and method/id lines at info; go test ./pkg/server/... passes.