feat(05-04): implement attach File, Thumb, blob bucket, system_files migration

- Winter-exact thumb filename and 3x3 partition with lazy imaging resize
- gocloud.dev/blob fileblob/memblob; empty bucket_url fails boot
- lagoon.Migrate runs system_files before every plugin set

go.mod

@@ -3,6 +3,7 @@ module git.golem15.com/golem15/summercms
 go 1.27.0
 
 require (
+	github.com/disintegration/imaging v1.6.2
 	github.com/fsnotify/fsnotify v1.10.1
 	github.com/go-gormigrate/gormigrate/v2 v2.1.7
 	github.com/go-playground/validator/v10 v10.30.4
@@ -96,6 +97,7 @@ require (
 	go.opentelemetry.io/otel/trace v1.44.0 // indirect
 	go.yaml.in/yaml/v3 v3.0.4 // indirect
 	golang.org/x/crypto v0.55.0 // indirect
+	golang.org/x/image v0.0.0-20191009234506-e7c1f5e7dbb8 // indirect
 	golang.org/x/net v0.57.0 // indirect
 	golang.org/x/sync v0.22.0 // indirect
 	golang.org/x/sys v0.48.0 // indirect