add debug mode and update readme (#805)

Fix #456
Fix #207

Reviewed-on: https://gitea.com/gitea/tea/pulls/805

modules/debug/debug.go

@@ -0,0 +1,44 @@
+// Copyright 2025 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package debug
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/urfave/cli/v3"
+)
+
+var debug bool
+
+// IsDebug returns true if debug mode is enabled
+func IsDebug() bool {
+	return debug
+}
+
+// SetDebug sets the debug mode
+func SetDebug(on bool) {
+	debug = on
+}
+
+// Printf prints debug information if debug mode is enabled
+func Printf(info string, args ...any) {
+	if debug {
+		fmt.Printf("DEBUG: "+info+"\n", args...)
+	}
+}
+
+// CliFlag returns the CLI flag for debug mode
+func CliFlag() cli.Flag {
+	return &cli.BoolFlag{
+		Name:    "debug",
+		Aliases: []string{"vvv"},
+		Usage:   "Enable debug mode",
+		Value:   false,
+		Action: func(ctx context.Context, cmd *cli.Command, v bool) error {
+			SetDebug(v)
+			return nil
+		},
+	}
+}