feat(user): Personal access tokens can be regenerated (#38907)

Lets users regenerate a personal access token's value in place, keeping
its name and scopes, instead of deleting and recreating it. Useful when
a token was shared with a third party (e.g. an AI agent) and needs to
be invalidated immediately without redoing scope selection.

Follows the same pattern already used for OAuth2 application client
secrets (`GenerateClientSecret`/`RegenerateSecret`).

**Testing**: added a model unit test and a web integration test;
manually
verified in the running dev server that the old token stops
authenticating
and the new one works immediately after regenerating.

<img width="1040" height="245" alt="image"
src="https://github.com/user-attachments/assets/4de0d8b4-1fc4-49cf-a859-95e24d0b2c0a"
/>

Fixes #38683.

---------

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

routers/api/actions/runner/interceptor.go

@@ -5,7 +5,6 @@ package runner
 
 import (
 	"context"
-	"crypto/subtle"
 	"errors"
 	"strings"
 	"time"
@@ -43,7 +42,7 @@ var withRunner = connect.WithInterceptors(connect.UnaryInterceptorFunc(func(unar
 			}
 			return nil, status.Error(codes.Internal, err.Error())
 		}
-		if subtle.ConstantTimeCompare([]byte(runner.TokenHash), []byte(auth_model.HashToken(token, runner.TokenSalt))) != 1 {
+		if !util.CryptoConstTimeEqual(runner.TokenHash, auth_model.HashToken(token, runner.TokenSalt)) {
 			return nil, status.Error(codes.Unauthenticated, "unregistered runner")
 		}