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/convert/__init__.py

@@ -0,0 +1 @@
+"""Type conversion plugins."""

workflow/plugins/python/convert/convert_parse_json.py

@@ -0,0 +1,13 @@
+"""Workflow plugin: parse JSON string."""
+import json
+
+
+def run(_runtime, inputs):
+    """Parse JSON string to object."""
+    text = inputs.get("text", "")
+
+    try:
+        result = json.loads(text)
+        return {"result": result}
+    except json.JSONDecodeError as e:
+        return {"result": None, "error": str(e)}

workflow/plugins/python/convert/convert_to_boolean.py

@@ -0,0 +1,11 @@
+"""Workflow plugin: convert to boolean."""
+
+
+def run(_runtime, inputs):
+    """Convert value to boolean."""
+    value = inputs.get("value")
+
+    if isinstance(value, str):
+        return {"result": value.lower() not in ("false", "0", "", "none", "null")}
+
+    return {"result": bool(value)}

workflow/plugins/python/convert/convert_to_dict.py

@@ -0,0 +1,17 @@
+"""Workflow plugin: convert to dictionary."""
+
+
+def run(_runtime, inputs):
+    """Convert value to dictionary."""
+    value = inputs.get("value")
+
+    if isinstance(value, dict):
+        return {"result": value}
+    elif isinstance(value, list):
+        # Convert list of [key, value] pairs to dict
+        try:
+            return {"result": dict(value)}
+        except (TypeError, ValueError):
+            return {"result": {}, "error": "Cannot convert list to dict"}
+    else:
+        return {"result": {}}

workflow/plugins/python/convert/convert_to_json.py

@@ -0,0 +1,14 @@
+"""Workflow plugin: convert to JSON string."""
+import json
+
+
+def run(_runtime, inputs):
+    """Convert value to JSON string."""
+    value = inputs.get("value")
+    indent = inputs.get("indent")
+
+    try:
+        result = json.dumps(value, indent=indent)
+        return {"result": result}
+    except (TypeError, ValueError) as e:
+        return {"result": None, "error": str(e)}

workflow/plugins/python/convert/convert_to_list.py

@@ -0,0 +1,17 @@
+"""Workflow plugin: convert to list."""
+
+
+def run(_runtime, inputs):
+    """Convert value to list."""
+    value = inputs.get("value")
+
+    if isinstance(value, list):
+        return {"result": value}
+    elif isinstance(value, (tuple, set)):
+        return {"result": list(value)}
+    elif isinstance(value, dict):
+        return {"result": list(value.items())}
+    elif value is None:
+        return {"result": []}
+    else:
+        return {"result": [value]}

workflow/plugins/python/convert/convert_to_number.py

@@ -0,0 +1,14 @@
+"""Workflow plugin: convert to number."""
+
+
+def run(_runtime, inputs):
+    """Convert value to number."""
+    value = inputs.get("value")
+    default = inputs.get("default", 0)
+
+    try:
+        if isinstance(value, str) and "." in value:
+            return {"result": float(value)}
+        return {"result": int(value)}
+    except (ValueError, TypeError):
+        return {"result": default, "error": "Cannot convert to number"}

workflow/plugins/python/convert/convert_to_string.py

@@ -0,0 +1,7 @@
+"""Workflow plugin: convert to string."""
+
+
+def run(_runtime, inputs):
+    """Convert value to string."""
+    value = inputs.get("value")
+    return {"result": str(value) if value is not None else ""}