fix(registry): log Unregister Close errors, add doc comments and 59 unit tests

Log close errors in Unregister instead of silently discarding them.
Add doc comments to all exported symbols across 20 registry files.
Add comprehensive tests covering base registry, all wrapper types,
hot-reload delegation, nil-fallback semantics, and global accessors.

registry/handler.go

@@ -5,12 +5,18 @@ import (
 	"github.com/go-gost/core/logger"
 )
 
+// NewHandler is a factory function that creates a new handler.Handler
+// from the given options.
 type NewHandler func(opts ...handler.Option) handler.Handler
 
+// handlerRegistry stores handler factory functions. Duplicate registrations
+// are treated as fatal errors (logger.Default().Fatal).
 type handlerRegistry struct {
 	registry[NewHandler]
 }
 
+// Register stores a handler factory under the given name. Calls Fatal on
+// duplicate registration since handler names must be unique at init time.
 func (r *handlerRegistry) Register(name string, v NewHandler) error {
 	if err := r.registry.Register(name, v); err != nil {
 		logger.Default().Fatal(err)