Run webhooks with the owner's rules again

The owner sets a webhook up and its URL is a secret, and a webhook run
already refuses every action that needs approval, so holding it to the
API write allowlist only broke the owner's own automations. Webhook runs
no longer count as external callers; schedules keep their caller rules.
The allowlist copy no longer names webhooks.

docsgpt/agents/headless_runner.py

@@ -90,7 +90,7 @@ def run_agent_headless(
     ``trace_user_id`` owns the trace when the run belongs to someone other
     than the agent's owner (a schedule a user set on a shared agent), so the
     trace is visible wherever that user sees the run; it defaults to the owner.
-    ``external_caller`` (a webhook, a schedule set through the API) and
+    ``external_caller`` (a schedule set through the API) and
     ``public_link_caller`` (a schedule a public-link user set) mark a run for
     someone who can't approve for the owner: writes on the owner's accounts
     and credentials then run only when the agent's API write allowlist has