SWAIG examples: standardize webhook auth on user:pass@ URL form; add missing defaults reference page (404)

[briankwest]

Problem

1. The SWAIG docs show two different auth parameter spellings in examples: /docs/swml/reference/calling/ai/swaig/functions uses web_hook_auth_pass (YAML and JSON examples); /docs/swml/reference/calling/ai/swaig/includes uses web_hook_auth_password (example and prose). Neither is formally documented as a parameter anywhere — they exist only inside examples — leaving readers to guess which spelling works, with authentication silently at stake.
2. /docs/swml/reference/calling/ai/swaig/defaults returns 404, while the examples on the pages above use a defaults object.

Fix

1. Standardize all SWAIG auth examples on credentials embedded in the URL: "web_hook_url": "https://user:pass@example.com/swaig". Note that the platform parses the userinfo and sends it as an Authorization header on the request (it does not remain on the request line). Remove the web_hook_auth_* parameter spellings from examples.
2. Pair this with a note that the SWML document then contains credentials and must itself be served from an authenticated endpoint (see the SWML security-note issue).
3. Create a real reference page for the SWAIG defaults object (fixing the 404) — it is where a shared web_hook_url belongs.