fix: resolve symlinked plugin directories in GetPluginVersion (#2661)

In nix/devbox environments, helm plugin directories are typically
symlinks into the Nix store. GetPluginVersion used entry.IsDir()
which does not follow symlinks, causing the plugin to be reported
as not installed. Follow symlinks with os.Stat before skipping
non-directory entries.

Signed-off-by: Shane Starcher <shane.starcher@gmail.com>
Co-authored-by: Shane Starcher <shane.starcher@gmail.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

pkg/helmexec/exec.go

@@ -141,7 +141,14 @@ func GetPluginVersion(name, pluginsDir string) (*semver.Version, error) {
 		}
 
 		for _, entry := range entries {
-			if !entry.IsDir() {
+			isDir := entry.IsDir()
+			if !isDir && entry.Type()&os.ModeSymlink != 0 {
+				info, err := os.Stat(filepath.Join(dir, entry.Name()))
+				if err == nil {
+					isDir = info.IsDir()
+				}
+			}
+			if !isDir {
 				continue
 			}