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/extends/base-module.yaml

@@ -0,0 +1,33 @@
+kind: module
+name: base-module
+description: Base module for testing inheritance
+
+params:
+  - name: target
+    type: string
+    required: true
+  - name: threads
+    type: string
+    default: "10"
+  - name: timeout
+    type: string
+    default: "3600"
+
+dependencies:
+  commands:
+    - echo
+  files:
+    - /bin/bash
+
+steps:
+  - name: step-one
+    type: bash
+    command: echo "Step one for {{target}}"
+
+  - name: step-two
+    type: bash
+    command: echo "Step two with threads={{threads}}"
+
+  - name: step-three
+    type: bash
+    command: echo "Step three"