feat: Add Python plugins from AutoMetabuilder + restructure workflow folder

Restructure workflow/ for multi-language plugin support:
- Rename src/ to core/ (engine code: DAG executor, registry, types)
- Create executor/{cpp,python,ts}/ for language-specific runtimes
- Consolidate plugins to plugins/{ts,python}/ by language then category

Add 80+ Python plugins from AutoMetabuilder in 14 categories:
- control: bot control, switch logic, state management
- convert: type conversions (json, boolean, dict, list, number, string)
- core: AI requests, context management, tool calls
- dict: dictionary operations (get, set, keys, values, merge)
- list: list operations (concat, find, sort, slice, filter)
- logic: boolean logic (and, or, xor, equals, comparisons)
- math: arithmetic operations (add, subtract, multiply, power, etc.)
- string: string manipulation (concat, split, replace, format)
- notifications: Slack, Discord integrations
- test: assertion helpers and test suite runner
- tools: file operations, git, docker, testing utilities
- utils: filtering, mapping, reducing, condition branching
- var: variable store operations (get, set, delete, exists)
- web: Flask server, environment variables, JSON handling

Add language executor runtimes:
- TypeScript: direct import execution (default, fast startup)
- Python: child process with JSON stdin/stdout communication
- C++: placeholder for native FFI bindings (Phase 3)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

workflow/plugins/python/dict/__init__.py

@@ -0,0 +1 @@
+"""Dictionary manipulation plugins."""

workflow/plugins/python/dict/dict_get.py

@@ -0,0 +1,14 @@
+"""Workflow plugin: get value from dictionary."""
+
+
+def run(_runtime, inputs):
+    """Get value from dictionary by key."""
+    obj = inputs.get("object", {})
+    key = inputs.get("key")
+    default = inputs.get("default")
+
+    if not isinstance(obj, dict):
+        return {"result": default, "found": False}
+
+    result = obj.get(key, default)
+    return {"result": result, "found": key in obj}

workflow/plugins/python/dict/dict_items.py

@@ -0,0 +1,11 @@
+"""Workflow plugin: get dictionary items as key-value pairs."""
+
+
+def run(_runtime, inputs):
+    """Get dictionary items as list of [key, value] pairs."""
+    obj = inputs.get("object", {})
+
+    if not isinstance(obj, dict):
+        return {"result": []}
+
+    return {"result": [[k, v] for k, v in obj.items()]}

workflow/plugins/python/dict/dict_keys.py

@@ -0,0 +1,11 @@
+"""Workflow plugin: get dictionary keys."""
+
+
+def run(_runtime, inputs):
+    """Get all keys from dictionary."""
+    obj = inputs.get("object", {})
+
+    if not isinstance(obj, dict):
+        return {"result": []}
+
+    return {"result": list(obj.keys())}

workflow/plugins/python/dict/dict_merge.py

@@ -0,0 +1,13 @@
+"""Workflow plugin: merge dictionaries."""
+
+
+def run(_runtime, inputs):
+    """Merge multiple dictionaries."""
+    objects = inputs.get("objects", [])
+    result = {}
+
+    for obj in objects:
+        if isinstance(obj, dict):
+            result.update(obj)
+
+    return {"result": result}

workflow/plugins/python/dict/dict_set.py

@@ -0,0 +1,15 @@
+"""Workflow plugin: set value in dictionary."""
+
+
+def run(_runtime, inputs):
+    """Set value in dictionary by key."""
+    obj = inputs.get("object", {})
+    key = inputs.get("key")
+    value = inputs.get("value")
+
+    if not isinstance(obj, dict):
+        obj = {}
+
+    result = dict(obj)
+    result[key] = value
+    return {"result": result}

workflow/plugins/python/dict/dict_values.py

@@ -0,0 +1,11 @@
+"""Workflow plugin: get dictionary values."""
+
+
+def run(_runtime, inputs):
+    """Get all values from dictionary."""
+    obj = inputs.get("object", {})
+
+    if not isinstance(obj, dict):
+        return {"result": []}
+
+    return {"result": list(obj.values())}