Add IP address tracking to session logs and metrics

This commit implements IP address tracking across the transport layer:

Changes:
- Added ipAddress field to SessionMetadata interface for session-level tracking
- Added uniqueIps count to TransportMetrics for aggregated statistics
- Implemented extractIpAddress() helper to parse x-forwarded-for and x-real-ip headers
- Updated SSE transport to capture and store IP addresses on connection
- Updated stateless HTTP transport to track IPs in analytics sessions
- Added unique IP count display to transport metrics UI
- Added IP Address column to sessions table in UI

The implementation efficiently tracks unique IPs using a Set data structure,
providing O(1) lookups while maintaining minimal memory overhead.

Author: claude