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_guild_test.go

@@ -117,16 +117,11 @@ func TestGuildRankCalculation(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			originalConfig := _config.ErupeConfig.RealClientMode
-			defer func() { _config.ErupeConfig.RealClientMode = originalConfig }()
-
-			_config.ErupeConfig.RealClientMode = tt.config
-
 			guild := &Guild{
 				RankRP: tt.rankRP,
 			}
 
-			rank := guild.Rank()
+			rank := guild.Rank(tt.config)
 			if rank != tt.wantRank {
 				t.Errorf("guild rank calculation: got %d, want %d for RP %d", rank, tt.wantRank, tt.rankRP)
 			}