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>

routers/api/v1/user/app.go

@@ -191,17 +191,9 @@ func DeleteAccessToken(ctx *context.APIContext) {
 			return
 		}
 	}
-	if tokenID == 0 {
-		ctx.APIErrorInternal(nil)
-		return
-	}
 
 	if err := auth_model.DeleteAccessTokenByID(ctx, tokenID, ctx.ContextUser.ID); err != nil {
-		if auth_model.IsErrAccessTokenNotExist(err) {
-			ctx.APIErrorNotFound()
-		} else {
-			ctx.APIErrorInternal(err)
-		}
+		ctx.APIErrorAuto(err)
 		return
 	}