feat: add configurable branch name whitespace replacement

Closes #2663

Adds a new config option `git.branchWhitespaceReplacement` that allows
users to specify the character used to replace whitespace in branch names.

By default, spaces are replaced with dashes ('-'), but teams that prefer
underscores or other characters can now configure this behavior.

Example config:
```yaml
git:
  branchWhitespaceReplacement: '_'
```

Changes:
- Added `BranchWhitespaceReplacement` config option (default: '-')
- Updated `SanitizedBranchName` to accept replacement parameter
- Added `SanitizedBranchNameWithConfig` helper method on RefsHelper
- Updated all callers to use the new config-aware method

pkg/config/user_config.go

@@ -306,6 +306,10 @@ type GitConfig struct {
 	CommitPrefixes map[string][]CommitPrefixConfig `yaml:"commitPrefixes"`
 	// See https://github.com/jesseduffield/lazygit/blob/master/docs/Config.md#predefined-branch-name-prefix
 	BranchPrefix string `yaml:"branchPrefix"`
+	// Specifies the character used to replace whitespace in branch names when creating new branches.
+	// By default, spaces are replaced with dashes ("-").
+	// Some teams use underscores ("_") or other characters.
+	BranchWhitespaceReplacement string `yaml:"branchWhitespaceReplacement"`
 	// If true, parse emoji strings in commit messages e.g. render :rocket: as 🚀
 	// (This should really be under 'gui', not 'git')
 	ParseEmoji bool `yaml:"parseEmoji"`
@@ -855,6 +859,7 @@ func GetDefaultConfig() *UserConfig {
 			DisableForcePushing:          false,
 			CommitPrefixes:               map[string][]CommitPrefixConfig(nil),
 			BranchPrefix:                 "",
+			BranchWhitespaceReplacement:  "-",
 			ParseEmoji:                   false,
 			TruncateCopiedCommitHashesTo: 12,
 		},

pkg/gui/controllers/branches_controller.go

@@ -707,7 +707,7 @@ func (self *BranchesController) rename(branch *models.Branch) error {
 			InitialContent: branch.Name,
 			HandleConfirm: func(newBranchName string) error {
 				self.c.LogAction(self.c.Tr.Actions.RenameBranch)
-				if err := self.c.Git().Branch.Rename(branch.Name, helpers.SanitizedBranchName(newBranchName)); err != nil {
+				if err := self.c.Git().Branch.Rename(branch.Name, self.c.Helpers().Refs.SanitizedBranchNameWithConfig(newBranchName)); err != nil {
 					return err
 				}
 

pkg/gui/controllers/helpers/refs_helper.go

@@ -366,7 +366,7 @@ func (self *RefsHelper) NewBranch(from string, fromFormattedName string, suggest
 		InitialContent: suggestedBranchName,
 		HandleConfirm: func(response string) error {
 			self.c.LogAction(self.c.Tr.Actions.CreateBranch)
-			newBranchName := SanitizedBranchName(response)
+			newBranchName := self.SanitizedBranchNameWithConfig(response)
 			newBranchFunc := self.c.Git().Branch.New
 			if newBranchName != suggestedBranchName {
 				newBranchFunc = self.c.Git().Branch.NewWithoutTracking
@@ -429,7 +429,7 @@ func (self *RefsHelper) MoveCommitsToNewBranch() error {
 			InitialContent: suggestedBranchName,
 			HandleConfirm: func(response string) error {
 				self.c.LogAction(self.c.Tr.MoveCommitsToNewBranch)
-				newBranchName := SanitizedBranchName(response)
+				newBranchName := self.SanitizedBranchNameWithConfig(response)
 				return self.c.WithWaitingStatus(self.c.Tr.MovingCommitsToNewBranchStatus, func(gocui.Task) error {
 					return f(newBranchName)
 				})
@@ -576,10 +576,20 @@ func (self *RefsHelper) CanMoveCommitsToNewBranch() *types.DisabledReason {
 	return nil
 }
 
-// SanitizedBranchName will remove all spaces in favor of a dash "-" to meet
-// git's branch naming requirement.
-func SanitizedBranchName(input string) string {
-	return strings.ReplaceAll(input, " ", "-")
+// SanitizedBranchName will remove all spaces in favor of the specified replacement
+// character to meet git's branch naming requirement.
+func SanitizedBranchName(input string, replacement string) string {
+	return strings.ReplaceAll(input, " ", replacement)
+}
+
+// SanitizedBranchNameWithConfig returns a sanitized branch name using the
+// user's configured whitespace replacement character.
+func (self *RefsHelper) SanitizedBranchNameWithConfig(input string) string {
+	replacement := self.c.UserConfig().Git.BranchWhitespaceReplacement
+	if replacement == "" {
+		replacement = "-"
+	}
+	return SanitizedBranchName(input, replacement)
 }
 
 // Checks if the given branch name is a remote branch, and returns the name of