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/tools/__init__.py

@@ -0,0 +1 @@
+"""External tool integration plugins."""

workflow/plugins/python/tools/tools_create_branch.py

@@ -0,0 +1,11 @@
+"""Workflow plugin: create branch."""
+
+
+def run(runtime, inputs):
+    """Create a branch via tool runner."""
+    result = runtime.tool_runner.call(
+        "create_branch",
+        branch_name=inputs.get("branch_name"),
+        base_branch=inputs.get("base_branch", "main")
+    )
+    return {"result": result}

workflow/plugins/python/tools/tools_create_pull_request.py

@@ -0,0 +1,13 @@
+"""Workflow plugin: create pull request."""
+
+
+def run(runtime, inputs):
+    """Create a pull request via tool runner."""
+    result = runtime.tool_runner.call(
+        "create_pull_request",
+        title=inputs.get("title"),
+        body=inputs.get("body"),
+        head_branch=inputs.get("head_branch"),
+        base_branch=inputs.get("base_branch", "main")
+    )
+    return {"result": result}

workflow/plugins/python/tools/tools_list_files.py

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+"""Workflow plugin: list files."""
+
+
+def run(runtime, inputs):
+    """List files via tool runner."""
+    result = runtime.tool_runner.call("list_files", directory=inputs.get("path", "."))
+    return {"files": result}

workflow/plugins/python/tools/tools_read_file.py

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+"""Workflow plugin: read file."""
+
+
+def run(runtime, inputs):
+    """Read a file via tool runner."""
+    result = runtime.tool_runner.call("read_file", path=inputs.get("path"))
+    return {"content": result}

workflow/plugins/python/tools/tools_run_docker.py

@@ -0,0 +1,59 @@
+"""Workflow plugin: run command in Docker container."""
+import subprocess
+import os
+import logging
+
+logger = logging.getLogger("metabuilder.docker")
+
+
+def _run_command_in_docker(image: str, command: str, volumes: dict = None, workdir: str = None):
+    """Run a command inside a Docker container.
+
+    :param image: Docker image to use.
+    :param command: Command to execute.
+    :param volumes: Dictionary of volume mappings {host_path: container_path}.
+    :param workdir: Working directory inside the container.
+    :return: Standard output of the command.
+    """
+    docker_command = ["docker", "run", "--rm"]
+
+    if volumes:
+        for host_path, container_path in volumes.items():
+            docker_command.extend(["-v", f"{os.path.abspath(host_path)}:{container_path}"])
+
+    if workdir:
+        docker_command.extend(["-w", workdir])
+
+    docker_command.append(image)
+    docker_command.extend(["sh", "-c", command])
+
+    logger.info(f"Executing in Docker ({image}): {command}")
+    result = subprocess.run(docker_command, capture_output=True, text=True, check=False)
+
+    output = result.stdout
+    if result.stderr:
+        output += "\n" + result.stderr
+
+    logger.info(output)
+    return output
+
+
+def run(_runtime, inputs):
+    """Run a command inside a Docker container.
+
+    Inputs:
+    - image: Docker image to use
+    - command: Command to execute
+    - volumes: Optional dict of volume mappings {host_path: container_path}
+    - workdir: Optional working directory inside the container
+    """
+    image = inputs.get("image")
+    command = inputs.get("command")
+    volumes = inputs.get("volumes")
+    workdir = inputs.get("workdir")
+
+    if not image or not command:
+        return {"error": "Both 'image' and 'command' are required"}
+
+    output = _run_command_in_docker(image, command, volumes, workdir)
+    return {"output": output}

workflow/plugins/python/tools/tools_run_lint.py

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+"""Workflow plugin: run lint."""
+
+
+def run(runtime, inputs):
+    """Run lint via tool runner."""
+    result = runtime.tool_runner.call("run_lint", path=inputs.get("path", "src"))
+    return {"results": result}

workflow/plugins/python/tools/tools_run_tests.py

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+"""Workflow plugin: run tests."""
+
+
+def run(runtime, inputs):
+    """Run tests via tool runner."""
+    result = runtime.tool_runner.call("run_tests", path=inputs.get("path", "tests"))
+    return {"results": result}