- Centralize environment variable loading in config.MustLoad
- Parse and validate all env vars once at initialization
- Make config fields private and read-only
- Remove public Getenv usage in favor of typed accessors
- Improve validation and initialization order
- Normalize enum naming to be idiomatic and avoid constant collisions
- Replace init() with config.Load() function when loading env variables
- Inject portRegistry into session, server, and lifecycle structs
- Inject sessionRegistry directly into interaction and lifecycle
- Remove SetSessionRegistry function and global port variables
- Pass ssh.Conn directly to forwarder constructor instead of lifecycle interface
- Pass user and closeFunc callback to interaction constructor instead of lifecycle interface
- Eliminate circular dependencies between lifecycle, forwarder, and interaction
- Remove setter methods (SetLifecycle) from forwarder and interaction interfaces
