feat: add LLM step executor with vision and tool support, event workflow system, and inheritance

- Add LLM executor supporting OpenAI vision, tool calling, embeddings, and structured outputs
- Introduce event emitter/receiver workflows with deduplication and filtering (generate_event functions)
- Add workflow extends/override system enabling inheritance chains and step merge modes
- Update function naming to snake_case across all testdata (fileExists→file_exists, etc.)
- Add comprehensive test fixtures for linter, events, CDN, step dependencies, and extends workflows

internal/executor/remote_bash_executor.go

@@ -15,11 +15,11 @@ import (
 
 // RemoteBashExecutor executes remote-bash steps on Docker/SSH runners
 type RemoteBashExecutor struct {
-	templateEngine *template.Engine
+	templateEngine template.TemplateEngine
 }
 
 // NewRemoteBashExecutor creates a new remote bash executor
-func NewRemoteBashExecutor(engine *template.Engine) *RemoteBashExecutor {
+func NewRemoteBashExecutor(engine template.TemplateEngine) *RemoteBashExecutor {
 	return &RemoteBashExecutor{
 		templateEngine: engine,
 	}