Feat v0.9.5 typed forms SDK primitive

Extract typed form system from models/workflow.go into standalone
server/forms/ package. Any package can now declare and validate
forms, not just workflow stages.

- New server/forms/ package (types + validation + condition evaluator)
- REST POST /api/v1/forms/validate endpoint
- Starlark forms.validate(template, data) module
- Frontend sw.forms.render(), .validate(), .validateRemote()
- Manifest form_template accepted at package level
- 16 new tests (12 forms + 4 Starlark module)

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

server/sandbox/runner.go

@@ -417,6 +417,9 @@ func (r *Runner) buildModulesWithLibCtx(ctx context.Context, packageID string, m
 				})
 			}
 
+		case models.ExtPermFormValidate:
+			modules["forms"] = BuildFormsModule(ctx)
+
 		case models.ExtPermBatchExec:
 			hasBatchExec = true
 		}