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/math/math_add/factory.py

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

workflow/plugins/python/math/math_add/math_add.py

@@ -1,7 +1,19 @@
 """Workflow plugin: add numbers."""
 
+from ...base import NodeExecutor
 
-def run(_runtime, inputs):
-    """Add two or more numbers."""
-    numbers = inputs.get("numbers", [])
-    return {"result": sum(numbers)}
+
+class MathAdd(NodeExecutor):
+    """Add numbers together."""
+
+    node_type = "math.add"
+    category = "math"
+    description = "Add numbers together"
+
+    def execute(self, inputs, runtime=None):
+        numbers = inputs.get("numbers", inputs.get("values", []))
+        try:
+            result = sum(float(n) for n in numbers)
+            return {"result": result}
+        except (ValueError, TypeError) as e:
+            return {"error": str(e)}

workflow/plugins/python/math/math_add/package.json

@@ -1,13 +1,16 @@
 {
   "name": "@metabuilder/math_add",
   "version": "1.0.0",
-  "description": "math_add plugin",
+  "description": "Add numbers together",
   "author": "MetaBuilder",
   "license": "MIT",
   "keywords": ["math", "workflow", "plugin"],
   "main": "math_add.py",
+  "files": ["math_add.py", "factory.py"],
   "metadata": {
     "plugin_type": "math.add",
-    "category": "math"
+    "category": "math",
+    "class": "MathAdd",
+    "entrypoint": "execute"
   }
 }