A webhook node parses its payload template as JSON before resolving
placeholders, so a template with unquoted {{ }} placeholders or any malformed
JSON could be saved, tested, and activated — only to fail midway through a run.
Reject it up front instead: AutomationConfigValidator is the single source of
truth for per-node config issues (keyed to the field the editor surfaces them
under), enforced on save (field errors), on activate, and before a test run.
The editor mirrors the check to disable Test/Activate with a clear reason, and
the test panel now surfaces the server's message instead of a generic toast.
2bd2e72656