fix: redirect early CLI console logger to stderr (#37507)

When running `gitea dump` with output routed to stdout (--file -),
deprecation warnings from loadAvatarsFrom were written to stdout,
corrupting the archive stream.

Root cause: PrepareConsoleLoggerLevel (called in app.Before) sets up a
console logger via SetConsoleLogger, which used WriterConsoleOption{}
defaulting Stderr to false (i.e. stdout). This logger is installed
before the dump subcommand can redirect logging to stderr in runDump.

Fix: use WriterConsoleOption{Stderr: true} in SetConsoleLogger so all
early CLI diagnostic output goes to stderr from the start. This is
correct for all subcommands — diagnostic/log output should never pollute
stdout.

---------

Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Nicolas <bircni@icloud.com>

cmd/helper.go

@@ -134,7 +134,7 @@ func PrepareConsoleLoggerLevel(defaultLevel log.Level) func(context.Context, *cl
 		if globalBool(c, "debug") || globalBool(c, "verbose") {
 			level = log.TRACE
 		}
-		log.SetConsoleLogger(log.DEFAULT, "console-default", level)
+		log.SetupStderrLogger(log.DEFAULT, "console-stderr", level)
 		return ctx, nil
 	}
 }