chore(constants): introduce ExtBat and replace bare ".bat" literals

The `goconst` linter flagged ".bat" as a repeated string literal across
manager.go, manager_test.go, and path.go. Add `constants.ExtBat`
alongside the existing ExtExe / ExtCmd constants and replace the bare
literals (and the bare ".exe"/".cmd" alongside them in the same files)
with the named constants.

Author: CalvinAllen

src/internal/constants/platform.go

@@ -34,4 +34,5 @@ const (
 const (
 	ExtExe = ".exe"
 	ExtCmd = ".cmd"
+	ExtBat = ".bat"
 )

src/internal/path/path.go

@@ -180,7 +180,7 @@ func LookPathExcludingShims(execName string) string {
 func findExecutableInDir(dir, execName string) string {
 	if runtime.GOOS == constants.OSWindows {
 		// Windows: try .exe, .cmd, .bat extensions
-		for _, ext := range []string{".exe", ".cmd", ".bat"} {
+		for _, ext := range []string{constants.ExtExe, constants.ExtCmd, constants.ExtBat} {
 			candidate := filepath.Join(dir, execName+ext)
 			if info, err := os.Stat(candidate); err == nil && !info.IsDir() {
 				return candidate

src/internal/shim/manager.go

@@ -169,7 +169,7 @@ func (m *Manager) ListShims() ([]string, error) {
 			if runtime.GOOS == constants.OSWindows {
 				ext := filepath.Ext(name)
 				// Skip .cmd/.bat wrappers — only list .exe shims
-				if ext == constants.ExtCmd || ext == ".bat" {
+				if ext == constants.ExtCmd || ext == constants.ExtBat {
 					continue
 				}
 				name = name[:len(name)-len(ext)]
@@ -397,7 +397,7 @@ func findExecutables(dir string) ([]string, error) {
 		// On Windows, check for executable extensions
 		if runtime.GOOS == constants.OSWindows {
 			ext := filepath.Ext(name)
-			if ext == ".exe" || ext == ".cmd" || ext == ".bat" {
+			if ext == constants.ExtExe || ext == constants.ExtCmd || ext == constants.ExtBat {
 				// Remove extension for shim name
 				baseName := name[:len(name)-len(ext)]
 				executables = append(executables, baseName)

src/internal/shim/manager_test.go

@@ -426,7 +426,7 @@ func TestListShims_SkipsCmdFiles(t *testing.T) {
 		}
 		name := entry.Name()
 		ext := filepath.Ext(name)
-		if ext == constants.ExtCmd || ext == ".bat" {
+		if ext == constants.ExtCmd || ext == constants.ExtBat {
 			continue
 		}
 		shims = append(shims, name[:len(name)-len(ext)])