chore: misc go 1.27 tweaks (#39069)

Follow-up to https://github.com/go-gitea/gitea/pull/39068, which
disabled `modernize` entirely.

- re-enable `modernize`, with only the new `embedlit` rule disabled. It
flattens embedded struct literals across ~145 files, and orphans imports
in 6 of them that the fixer does not remove
- apply the rest of the suite: `errors.AsType`, `reflect.TypeAssert`,
`strings.Cut`, and dropping the legacy import comment
- use the new stdlib `uuid` package, `github.com/google/uuid` becomes
indirect
- use `strings.CutLast` in place of manual `LastIndex` slicing in label
scopes, email domains and the diff tree list
- take the header lint skip dirs from the `go.mod` `ignore` directive
and skip dot-directories, instead of hardcoding the list

Assisted-by: Claude Code:claude-opus-5

models/repo/repo_list.go

@@ -617,7 +617,7 @@ func searchRepositoryByCondition(ctx context.Context, opts SearchRepoOptions, co
 		args = append(args, opts.PriorityOwnerID)
 	} else if strings.Count(opts.Keyword, "/") == 1 {
 		// With "owner/repo" search times, prioritise results which match the owner field
-		orgName := strings.Split(opts.Keyword, "/")[0]
+		orgName, _, _ := strings.Cut(opts.Keyword, "/")
 		orderBy = db.SearchOrderBy(fmt.Sprintf("CASE WHEN owner_name LIKE ? THEN 0 ELSE 1 END, %s", orderBy))
 		args = append(args, orgName)
 	}

models/repo/upload.go

@@ -11,13 +11,12 @@ import (
 	"mime/multipart"
 	"os"
 	"path/filepath"
+	"uuid"
 
 	"gitea.dev/models/db"
 	"gitea.dev/modules/log"
 	"gitea.dev/modules/setting"
 	"gitea.dev/modules/util"
-
-	gouuid "github.com/google/uuid"
 )
 
 // ErrUploadNotExist represents a "UploadNotExist" kind of error.
@@ -60,7 +59,7 @@ func (upload *Upload) LocalPath() string {
 // NewUpload creates a new upload object.
 func NewUpload(ctx context.Context, name string, buf []byte, file multipart.File) (_ *Upload, err error) {
 	upload := &Upload{
-		UUID: gouuid.New().String(),
+		UUID: uuid.New().String(),
 		Name: name,
 	}