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/service.go

@@ -4,6 +4,9 @@ import (
 	"github.com/go-gost/core/service"
 )
 
+// serviceRegistry stores service.Service instances.
+// It uses the base registry methods without a wrapper since services
+// are looked up directly by name during startup.
 type serviceRegistry struct {
 	registry[service.Service]
 }