refactor(workflow): convert all plugins to class/struct + factory pattern

- Python: class extending NodeExecutor + factory.py (80+ plugins)
- TypeScript: class implements NodeExecutor + factory.ts (7 groups, 116 classes)
- Go: struct with methods + factory.go (36 plugins)
- Rust: struct impl NodeExecutor trait + factory.rs (54 plugins)
- Mojo: struct + factory.mojo (11 plugins)

All package.json files now include:
- files array listing source files
- metadata.class/struct field
- metadata.entrypoint field

This enables a unified plugin loading system across all languages
with no import side effects (Spring-style DI pattern).

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

workflow/plugins/python/web/web_start_server/factory.py

@@ -0,0 +1,7 @@
+"""Factory for WebStartServer plugin."""
+
+from .web_start_server import WebStartServer
+
+
+def create():
+    return WebStartServer()

workflow/plugins/python/web/web_start_server/package.json

@@ -1,13 +1,16 @@
 {
   "name": "@metabuilder/web_start_server",
   "version": "1.0.0",
-  "description": "web_start_server plugin",
+  "description": "Start the Flask web server",
   "author": "MetaBuilder",
   "license": "MIT",
   "keywords": ["web", "workflow", "plugin"],
   "main": "web_start_server.py",
+  "files": ["web_start_server.py", "factory.py"],
   "metadata": {
     "plugin_type": "web.start_server",
-    "category": "web"
+    "category": "web",
+    "class": "WebStartServer",
+    "entrypoint": "execute"
   }
 }

workflow/plugins/python/web/web_start_server/web_start_server.py

@@ -1,26 +1,38 @@
 """Workflow plugin: start Flask server."""
 
+from ...base import NodeExecutor
 
-def run(runtime, inputs):
-    """Start the Flask web server.
 
-    Inputs:
-        host: Host address (default: 0.0.0.0)
-        port: Port number (default: 8000)
-        debug: Enable debug mode (default: False)
+class WebStartServer(NodeExecutor):
+    """Start the Flask web server."""
 
-    Returns:
-        dict: Success indicator (note: this blocks until server stops)
-    """
-    app = runtime.context.get("flask_app")
-    if not app:
-        return {"error": "Flask app not found in context. Run web.create_flask_app first."}
+    node_type = "web.start_server"
+    category = "web"
+    description = "Start the Flask web server"
 
-    host = inputs.get("host", "0.0.0.0")
-    port = inputs.get("port", 8000)
-    debug = inputs.get("debug", False)
+    def execute(self, inputs, runtime=None):
+        """Start the Flask web server.
 
-    # This will block until the server is stopped
-    app.run(host=host, port=port, debug=debug)
+        Inputs:
+            host: Host address (default: 0.0.0.0)
+            port: Port number (default: 8000)
+            debug: Enable debug mode (default: False)
 
-    return {"result": "Server stopped"}
+        Returns:
+            dict: Success indicator (note: this blocks until server stops)
+        """
+        if runtime is None:
+            return {"error": "Runtime context required"}
+
+        app = runtime.context.get("flask_app")
+        if not app:
+            return {"error": "Flask app not found in context. Run web.create_flask_app first."}
+
+        host = inputs.get("host", "0.0.0.0")
+        port = inputs.get("port", 8000)
+        debug = inputs.get("debug", False)
+
+        # This will block until the server is stopped
+        app.run(host=host, port=port, debug=debug)
+
+        return {"result": "Server stopped"}