chore(go-update): migrate module path to dappco.re/go/update

Dropped the stale `core` segment per RFC. Updated go.mod + service.go
go:generate subpath + service_examples_test.go. Pre-existing go.mod
core-dep resolution gap (requires core@v0.3.1 which declares
forge.lthn.ai path) is unrelated and out of this ticket's scope.

Closes tasks.lthn.sh/view.php?id=762

Co-authored-by: Codex <noreply@openai.com>

go.mod

@@ -1,4 +1,4 @@
-module dappco.re/go/core/update
+module dappco.re/go/update
 
 go 1.26.0
 

service.go

@@ -1,4 +1,4 @@
-//go:generate go run dappco.re/go/core/update/build
+//go:generate go run dappco.re/go/update/build
 
 // Package updater provides functionality for self-updating Go applications.
 // It supports updates from GitHub releases and generic HTTP endpoints.

service_examples_test.go

@@ -4,7 +4,7 @@ import (
 	"fmt"
 	"log"
 
-	updater "dappco.re/go/core/update"
+	updater "dappco.re/go/update"
 )
 
 func ExampleNewUpdateService() {