refactor: drop logrus and other direct dependencies (#1319)

After https://gitea.com/gitea/runner/pulls/1304, logrus stayed only to forward logs from docker/cli and moby/go-archive. The runner used a small part of those: volume parsing, the build context tar, the `ssh://` connection and registry credentials. Own code that matches them replaces them, so logrus leaves the module graph. docker/cli stays for its logrus-free `opts` and `connhelper/ssh` packages.

Other dependencies that the standard library or existing ones cover go too: mergo, httprouter (replaced by `http.ServeMux`), retry-go, go-isatty, go-selinux, container-device-interface, gotest.tools and go-cmp (replaced by testify). The binary shrinks by 5%.

Behaviour differences:

1. An unreadable file in a build context is skipped with a warning, where go-archive left a truncated tar.
2. Build contexts no longer carry `security.capability` xattrs.
3. The cache and artifact servers answer HEAD on GET routes, and no longer redirect trailing slashes or answer OPTIONS.

*Written by Claude.*

---------

Co-authored-by: bircni <[email protected]>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1319
Reviewed-by: bircni <[email protected]>
Reviewed-by: Lunny Xiao <[email protected]>
Co-authored-by: silverwind <[email protected]>

internal/app/cmd/register.go

@@ -24,15 +24,15 @@ import (
 	"connectrpc.com/connect"
 	pingv1 "gitea.dev/actionslib/ping/v1"
 	runnerv1 "gitea.dev/actionslib/runner/v1"
-	"github.com/mattn/go-isatty"
 	"github.com/spf13/cobra"
+	"golang.org/x/term"
 )
 
 // runRegister registers a runner to the server
 func runRegister(ctx context.Context, regArgs *registerArgs, configFile *string) func(*cobra.Command, []string) error {
 	return func(cmd *cobra.Command, args []string) error {
 		logging.SetReportCaller(false)
-		isTerm := isatty.IsTerminal(os.Stdout.Fd())
+		isTerm := term.IsTerminal(int(os.Stdout.Fd()))
 		logging.SetTextFormat(logging.TextOptions{
 			DisableColors:    !isTerm,
 			DisableTimestamp: true,