feat(web): ES-module page lifecycle and one schema field model (stage 1) (#703)

Adds a native ES-module layer to the web UI (core/boot, registry, api, facade; window.LEDMatrix as the one global), a page lifecycle that the Cache tab is converted to as the reference, text/javascript serving and revalidation for unversioned module requests, and src/plugin_system/field_model.py with a parity test against the render_field macro. Also: the cache page toggles its grey 'Not configured' style instead of only adding it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web_interface/static/v3/plugins_manager.js

@@ -25,8 +25,12 @@
  *                      state_manager.js, install_manager.js, list_filter.js,
  *                      the widget bundle (web_interface/widget_bundle.py),
  *                      plugins_manager.js
+ *   end of <body>, type=module (deferred, runs last): js/core/boot.js --
+ *                      window.LEDMatrix and the page registry
  *   Tab partials arrive later through htmx; their inline scripts run on
- *   htmx:afterSwap (js/htmx-config.js).
+ *   htmx:afterSwap (js/htmx-config.js). A partial converted to a page module
+ *   (data-page root, js/pages/<name>.js) has no inline script; the registry
+ *   starts it (js/core/registry.js, docs/WEB_FRONTEND_ARCHITECTURE.md).
  *
  * Layout: a few handlers defined up front, outside any IIFE, because the
  * cards and other scripts call them through window (configurePlugin,