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

modules/web/handler.go

@@ -66,7 +66,7 @@ var (
 func preCheckHandler(fn reflect.Value, argsIn []reflect.Value) {
 	hasStatusProvider := false
 	for _, argIn := range argsIn {
-		if _, hasStatusProvider = argIn.Interface().(types.ResponseStatusProvider); hasStatusProvider {
+		if _, hasStatusProvider = reflect.TypeAssert[types.ResponseStatusProvider](argIn); hasStatusProvider {
 			break
 		}
 	}
@@ -119,7 +119,7 @@ func handleResponse(fn reflect.Value, ret []reflect.Value) {
 
 func hasResponseBeenWritten(argsIn []reflect.Value) bool {
 	for _, argIn := range argsIn {
-		if statusProvider, ok := argIn.Interface().(types.ResponseStatusProvider); ok {
+		if statusProvider, ok := reflect.TypeAssert[types.ResponseStatusProvider](argIn); ok {
 			if statusProvider.WrittenStatus() != 0 {
 				return true
 			}