chore(go): audit providers claudecode codex cursor gemini

Add managed_runtime.go (paths, config validation, identity, runtime file
changes, status checks) and shell_command.go (quoting, PowerShell
encoding, command parsing) and move the four providers onto them.

Claude-Session: https://claude.ai/code/session_01Agoc9bRVE9KL7mmWtey9Vq

cmd/elydora/plugins/augment_io.go

@@ -211,7 +211,7 @@ func resolveAugmentWrapperPaths(agentDirectory string) augmentWrapperPaths {
 }
 
 func requireAugmentAbsoluteNode(nodePath string) error {
-	if !filepath.IsAbs(nodePath) || !isClaudeNodeExecutable(nodePath) {
+	if !filepath.IsAbs(nodePath) || !isNodeExecutable(nodePath) {
 		return fmt.Errorf("Auggie hooks require an absolute Node.js executable path")
 	}
 	return nil