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

network/mhfpacket/msg_mhf_savedata.go

@@ -30,7 +30,7 @@ func (m *MsgMhfSavedata) Parse(bf *byteframe.ByteFrame, ctx *clientctx.ClientCon
 	m.AllocMemSize = bf.ReadUint32()
 	m.SaveType = bf.ReadUint8()
 	m.Unk1 = bf.ReadUint32()
-	if _config.ErupeConfig.RealClientMode >= _config.G1 {
+	if ctx.RealClientMode >= _config.G1 {
 		m.DataSize = bf.ReadUint32()
 	}
 	if m.DataSize == 0 { // seems to be used when DataSize = 0 rather than on savetype?