feat(mcp): refactor logging to use exchange for targeted client notifications

[tzolov]

Refactors the MCP logging system to use the exchange mechanism for sending logging notifications only to specific client sessions rather than broadcasting to all clients.

• Move logging notification delivery from server-wide broadcast to per-session exchange
• Implement per-session minimum logging level tracking and filtering
• Change setLoggingLevel from notification to request/response pattern
• Deprecate global server.loggingNotification in favor of exchange.loggingNotification
• Add integration test demonstrating filtered logging notifications

Resolves #131