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

test/testdata/workflows/test-complex-docker-workflow.yaml

@@ -87,7 +87,7 @@ steps:
   - name: verify-ports-file
     type: function
     log: "Verifying ports file exists"
-    function: fileExists("{{ports_file}}")
+    function: file_exists("{{ports_file}}")
     exports:
       ports_verified: "output"
 
@@ -150,7 +150,7 @@ steps:
   - name: read-subdomain-results
     type: function
     log: "Reading subdomain scan results"
-    function: readFile("{{output_dir}}/subdomain-results.txt")
+    function: read_file("{{output_dir}}/subdomain-results.txt")
     exports:
       scan_results: "output"
 
@@ -200,8 +200,8 @@ steps:
     type: function
     log: "Getting file statistics"
     parallel_functions:
-      - fileLength("{{output_dir}}/report.txt")
-      - fileExists("{{output_dir}}/all-ports.txt")
+      - file_length("{{output_dir}}/report.txt")
+      - file_exists("{{output_dir}}/all-ports.txt")
       - trim("  {{target}}  ")
     exports:
       file_stats: "output"