Feat v0.9.2 Starlark converter consolidation + snapshot cleanup (#75)

Consolidate duplicate Go↔Starlark converters into sandbox/convert.go
and snapshot parsers into models/snapshot.go. Standardize snapshot
creation on wrapped format. Net -393 lines across 21 files.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/sandbox/workflow_module.go

@@ -112,7 +112,7 @@ func workflowGetInstance(ctx context.Context, stores store.Stores) func(*starlar
 		if json.Unmarshal(inst.StageData, &dataMap) == nil {
 			starlarkData := starlark.NewDict(len(dataMap))
 			for k, v := range dataMap {
-				starlarkData.SetKey(starlark.String(k), goValToStarlark(v))
+				starlarkData.SetKey(starlark.String(k), GoToStarlark(v))
 			}
 			d.SetKey(starlark.String("stage_data"), starlarkData)
 		} else {
@@ -155,36 +155,5 @@ func workflowListInstances(ctx context.Context, stores store.Stores) func(*starl
 	}
 }
 
-// goValToStarlark converts a Go value to a Starlark value.
-func goValToStarlark(v interface{}) starlark.Value {
-	switch val := v.(type) {
-	case nil:
-		return starlark.None
-	case bool:
-		return starlark.Bool(val)
-	case float64:
-		if val == float64(int(val)) {
-			return starlark.MakeInt(int(val))
-		}
-		return starlark.Float(val)
-	case string:
-		return starlark.String(val)
-	case map[string]interface{}:
-		d := starlark.NewDict(len(val))
-		for k, v := range val {
-			d.SetKey(starlark.String(k), goValToStarlark(v))
-		}
-		return d
-	case []interface{}:
-		elems := make([]starlark.Value, len(val))
-		for i, v := range val {
-			elems[i] = goValToStarlark(v)
-		}
-		return starlark.NewList(elems)
-	default:
-		return starlark.String(fmt.Sprintf("%v", v))
-	}
-}
-
 // workflowRoute routes the workflow to a named stage.
 // Starlark: workflow.route(instance_id, target_stage, reason)