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-flow.yaml

@@ -0,0 +1,17 @@
+kind: flow
+name: base-flow
+description: Base flow for testing inheritance
+
+params:
+  - name: target
+    type: string
+    required: true
+
+modules:
+  - name: module-a
+    path: base-module
+
+  - name: module-b
+    path: base-module
+    depends_on:
+      - module-a

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"

test/testdata/workflows/extends/chain-a.yaml

@@ -0,0 +1,12 @@
+kind: module
+name: chain-a
+description: Chain test - root
+
+params:
+  - name: param-a
+    default: "from-a"
+
+steps:
+  - name: step-from-a
+    type: bash
+    command: echo "from chain-a"

test/testdata/workflows/extends/chain-b.yaml

@@ -0,0 +1,15 @@
+kind: module
+name: chain-b
+description: Chain test - middle
+extends: chain-a
+
+override:
+  params:
+    param-a:
+      default: "overridden-by-b"
+  steps:
+    mode: append
+    steps:
+      - name: step-from-b
+        type: bash
+        command: echo "from chain-b"

test/testdata/workflows/extends/chain-c.yaml

@@ -0,0 +1,15 @@
+kind: module
+name: chain-c
+description: Chain test - leaf
+extends: chain-b
+
+override:
+  params:
+    param-a:
+      default: "final-from-c"
+  steps:
+    mode: append
+    steps:
+      - name: step-from-c
+        type: bash
+        command: echo "from chain-c"

test/testdata/workflows/extends/child-flow.yaml

@@ -0,0 +1,13 @@
+kind: flow
+name: child-flow
+description: Child flow that extends base flow
+extends: base-flow
+
+override:
+  modules:
+    mode: append
+    modules:
+      - name: module-c
+        path: base-module
+        depends_on:
+          - module-b

test/testdata/workflows/extends/child-merge-steps.yaml

@@ -0,0 +1,18 @@
+kind: module
+name: child-merge-steps
+description: Child that merges steps (replace specific, remove some, add new)
+extends: base-module
+
+override:
+  steps:
+    mode: merge
+    steps:
+      - name: step-new
+        type: bash
+        command: echo "New step added"
+    remove:
+      - step-three
+    replace:
+      - name: step-two
+        type: bash
+        command: echo "Step two replaced with new command"

test/testdata/workflows/extends/child-override-steps.yaml

@@ -0,0 +1,15 @@
+kind: module
+name: child-override-steps
+description: Child that appends steps
+extends: base-module
+
+override:
+  params:
+    threads:
+      default: "20"
+  steps:
+    mode: append
+    steps:
+      - name: step-four
+        type: bash
+        command: echo "Step four added by child"

test/testdata/workflows/extends/child-prepend-steps.yaml

@@ -0,0 +1,12 @@
+kind: module
+name: child-prepend-steps
+description: Child that prepends steps
+extends: base-module
+
+override:
+  steps:
+    mode: prepend
+    steps:
+      - name: step-zero
+        type: bash
+        command: echo "Step zero prepended by child"

test/testdata/workflows/extends/child-replace-steps.yaml

@@ -0,0 +1,16 @@
+kind: module
+name: child-replace-steps
+description: Child that replaces all steps
+extends: base-module
+
+override:
+  steps:
+    mode: replace
+    steps:
+      - name: new-step-one
+        type: bash
+        command: echo "Completely new step one"
+
+      - name: new-step-two
+        type: bash
+        command: echo "Completely new step two"

test/testdata/workflows/extends/child-simple.yaml

@@ -0,0 +1,11 @@
+kind: module
+name: child-simple
+description: Simple child that only overrides params
+extends: base-module
+
+override:
+  params:
+    threads:
+      default: "5"
+    timeout:
+      default: "1800"

test/testdata/workflows/extends/circular-a.yaml

@@ -0,0 +1,9 @@
+kind: module
+name: circular-a
+description: Circular dependency test A
+extends: circular-b
+
+steps:
+  - name: step-a
+    type: bash
+    command: echo "A"

test/testdata/workflows/extends/circular-b.yaml

@@ -0,0 +1,9 @@
+kind: module
+name: circular-b
+description: Circular dependency test B
+extends: circular-a
+
+steps:
+  - name: step-b
+    type: bash
+    command: echo "B"

test/testdata/workflows/extends/kind-mismatch.yaml

@@ -0,0 +1,8 @@
+kind: flow
+name: kind-mismatch
+description: This flow tries to extend a module (should fail)
+extends: base-module
+
+modules:
+  - name: module-x
+    path: base-module