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/dbutils.go

@@ -105,7 +105,7 @@ func (s *Server) getUserRights(uid uint32) uint32 {
 	var rights uint32
 	if uid != 0 {
 		_ = s.db.QueryRow("SELECT rights FROM users WHERE id=$1", uid).Scan(&rights)
-		_, rights = mhfcourse.GetCourseStruct(rights)
+		_, rights = mhfcourse.GetCourseStruct(rights, s.erupeConfig.DefaultCourses)
 	}
 	return rights
 }