fix(mcp): use os.homedir() instead of literal '~' fallback

[ryjm]

Summary

path.join() doesn't expand tilde, so when process.env.HOME is undefined,
the fallback to '~' created literal directories named '~/' instead of
expanding to the user's home.

This caused the proliferation of confusing '~/' directories containing
.efrit/logs/. It's also kind of terrifying to try and remove.

Fix

• Import os module
• Use os.homedir() as fallback instead of literal '~' string

Before

const defaultLogFile = path.join(process.env['HOME'] || '~', '.efrit', 'logs', 'mcp-server.log');

After

const homeDir = process.env['HOME'] || os.homedir();
const defaultLogFile = path.join(homeDir, '.efrit', 'logs', 'mcp-server.log');