Remove legacy mode.

- Deleted the legacy WebSocket client implementation (`wstoclient.go`) and its test file (`wstoclient_test.go`).
- Removed legacy handling from the HTTP manager, including legacy proxy setup and routing.
- Cleaned up session management by removing legacy host checks and related functions.
- Eliminated the legacy WebRTC handler and its associated logic.
- Updated session interface to remove legacy methods.
- Removed legacy API documentation and configuration options from migration guide and help files.

server/pkg/types/session.go

@@ -69,7 +69,6 @@ type Session interface {
 	Profile() MemberProfile
 	State() SessionState
 	IsHost() bool
-	LegacyIsHost() bool
 	SetAsHost()
 	SetAsHostBy(session Session)
 	ClearHost()