Squarespace embed-widget integration (for directory treehouse #116)

**Scope narrowed 2026-05-04.** Originally proposed as a full Squarespace Commerce API integration (`nimsforestsquarespace` with Orders/Inventory/Products/Contacts sources). That scope is no longer needed — the driving use-case turned out to be the XR Valley company directory, which is being built as a reusable directory treehouse on org land instead (see #116).

What remains here is much smaller: making the directory treehouse's embed widget drop cleanly into Squarespace pages.

## Scope
- Verify `<script src="https://directory.{org}.tld/embed.js">` loads inside Squarespace's Code Block / Code Injection contexts (CSP, sandboxing, layout edge cases).
- Document the embed snippet for site editors (xrvalley.be first) — single copy/paste block, no Developer Mode required.
- Confirm featured-card layout works inside Squarespace section widths and on mobile.
- Capture any Squarespace-side caveats in a runbook (which block type, where to paste, how to update).

## Out of scope (was original scope, now dropped)
- Squarespace Commerce APIs (Orders/Inventory/Products/Contacts/Webhooks)
- A `nimsforestsquarespace` repo — not needed; the embed lives in `nimsforestdirectorytreehouse`.
- Any Squarespace-side data ingestion into NimsForest.

## Blocked by
- #116 — embed widget must exist before this can be tested.

## Docs (kept for reference if Commerce API integration is ever revived)
- https://developers.squarespace.com/commerce-apis/overview
- https://support.squarespace.com/hc/en-us/articles/41325887099533-Developer-Tools-APIs-at-Squarespace