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/channelserver/handlers_tower.go

@@ -75,7 +75,7 @@ func handleMsgMhfGetTowerInfo(s *Session, p mhfpacket.MHFPacket) {
 		}
 	}
 
-	if _config.ErupeConfig.RealClientMode <= _config.G7 {
+	if s.server.erupeConfig.RealClientMode <= _config.G7 {
 		towerInfo.Level = towerInfo.Level[:1]
 	}