docs: add doc.go files and godoc comments to all packages

Add package-level documentation (doc.go) to all 22 first-party
packages and godoc comments to ~150 previously undocumented
exported symbols across common/, network/, and server/.

server/channelserver/handlers_event.go

@@ -11,6 +11,7 @@ import (
 	"go.uber.org/zap"
 )
 
+// Event represents an in-game event entry.
 type Event struct {
 	EventType    uint16
 	Unk1         uint16