refactor(config): eliminate ErupeConfig global variable

Replace the mutable global `_config.ErupeConfig` with dependency
injection across 79 files. Config is now threaded through existing
paths: `ClientContext.RealClientMode` for packet encoding, `s.server.
erupeConfig` for channel handlers, and explicit parameters for utility
functions. This removes hidden coupling, enables test parallelism
without global save/restore, and prevents low-level packages from
reaching up to the config layer.

Key changes:
- Enrich ClientContext with RealClientMode for packet files
- Add mode parameter to CryptConn, mhfitem, mhfcourse functions
- Convert handlers_commands init() to lazy sync.Once initialization
- Delete global var, init(), and helper functions from config.go
- Update all tests to pass config explicitly

server/signserver/sign_server.go

@@ -101,7 +101,7 @@ func (s *Server) handleConnection(conn net.Conn) {
 		logger:    s.logger,
 		server:    s,
 		rawConn:   conn,
-		cryptConn: network.NewCryptConn(conn),
+		cryptConn: network.NewCryptConn(conn, s.erupeConfig.RealClientMode),
 	}
 
 	// Do the session's work.