chore(changeset): action body composite fix

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: os-zhuang

.changeset/studio-action-body-composite.md

@@ -0,0 +1,7 @@
+---
+"@objectstack/spec": patch
+---
+
+fix(spec): render action `body` as a composite editor (language + source) instead of a flat code field
+
+An action's `body` is a discriminated union (`HookBodySchema`), the same shape hooks use, but `action.form.ts` mapped the whole field to `{ widget: 'code' }`, so the Studio inspector fed the union object to a single JS editor and rendered `[object Object]`. The layout now mirrors the working `hook.form.ts`: a composite with a `language` select, a `source` code editor, and the L2-only capability/timeout knobs.