Host actions, Connect with Datalumo, and Woo sync

[jeffreyvr]

Summary

• Listens for confirmed Datalumo host actions: add_to_cart, view_cart, open_checkout, and open_page. Variable products return nested choices. Product pages send product_id as chat context.
• Connect with Datalumo starts a grant on the Datalumo app, then exchanges a one-time code. Manual setup is token-only via GET /api/v1/me. Widget keys and secrets are rejected in the token field.
• After connect, a short checklist covers what to sync, chat, and enhanced search. Tabs and the Need help sidebar stay hidden until setup is ready.
• The self-hosted Datalumo URL sits behind Using a self-hosted Datalumo? It opens when a non-cloud URL is already stored.
• WooCommerce products sync short description, product categories and tags, visible attributes, and SKU (including variations).
• Every first-party folder has a silence-is-golden index.php. Vendor copies are stamped on composer dump-autoload.

Pairs with datalumo/datalumo#5.

This PR is the product work. WordPress.org listing prep (drop the GitHub update checker, license, Plugin Check cleanups) stays on #2 for later.

Test plan

• Simple product: confirm add to cart from chat, cart has the line.
• Variable product with colour and size: pick both, cart line has both attributes.
• From a WordPress site, press Connect with Datalumo. Complete the grant and land back on Settings → Datalumo with a source and token stored.
• Cancel on the grant screen returns to Settings → Datalumo.
• Manual connect: paste an org API token (not a widget key) and Connect & test.
• Open Using a self-hosted Datalumo?, set a custom URL, and confirm connect hits that host.
• After connect, finish the checklist. Tabs and Need help appear only when setup is ready.
• Sync a variable product and confirm short description, categories, tags, visible attributes, and SKU are searchable.
• composer test