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/raviente.go

@@ -11,6 +11,7 @@ import (
 	"go.uber.org/zap"
 )
 
+// Raviente holds shared state for the Raviente siege event.
 type Raviente struct {
 	sync.Mutex
 	id       uint16