feat(api): add token introspection and self-deletion endpoint (#37995)

Adds a /api/v1/token endpoint that allows tokens to introspect and
delete themselves.
partially fixes: https://github.com/go-gitea/gitea/issues/33583

Assisted-by: Mistral Vibe:mistral-medium-3.5

---------

Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

services/auth/basic.go

@@ -5,6 +5,7 @@
 package auth
 
 import (
+	"errors"
 	"net/http"
 
 	actions_model "gitea.dev/models/actions"
@@ -104,8 +105,8 @@ func (b *Basic) VerifyAuthToken(req *http.Request, w http.ResponseWriter, store
 		store.GetData()["IsApiToken"] = true
 		store.GetData()["ApiTokenScope"] = token.Scope
 		return u, nil
-	} else if !auth_model.IsErrAccessTokenNotExist(err) && !auth_model.IsErrAccessTokenEmpty(err) {
-		log.Error("GetAccessTokenBySha: %v", err)
+	} else if !errors.Is(err, util.ErrNotExist) {
+		log.Error("GetAccessTokenBySHA: %v", err)
 	}
 
 	// check task token

services/auth/oauth2.go

@@ -128,7 +128,7 @@ func (o *OAuth2) userFromToken(ctx context.Context, tokenSHA string, store DataS
 	}
 	t, err := auth_model.GetAccessTokenBySHA(ctx, tokenSHA)
 	if err != nil {
-		if auth_model.IsErrAccessTokenNotExist(err) {
+		if errors.Is(err, util.ErrNotExist) {
 			// check task token
 			if task, err := actions_model.GetRunningTaskByToken(ctx, tokenSHA); err == nil {
 				log.Trace("Basic Authorization: Valid AccessToken for task[%d]", task.ID)