feat(web): the Display tab is an ES-module page, with a page-visibility service (stage 4) (#771)

* feat(web): the Display tab is an ES-module page, with a page-visibility service (stage 4)

- core/visibility.js: each page gets ctx.visibility (whileVisible, every,
  isVisible). Work registered there runs only while the page's tab is
  active and the browser tab visible, and ends when the page is swapped
  out. It reads the active tab from window.LEDVisibility, so it agrees
  with the classic partials. The registry gained a mountContext option for
  per-mount services.
- pages/display.js replaces display.html's two inline scripts. The 5 s
  sync status poll runs through ctx.visibility.every; the status and
  scroll-speed hint requests go through ctx.api with ctx.signal, as does
  the Vegas order widget's plugin-list request. The Advanced toggle is a
  delegated data-action; window.updateSyncUI is a deprecated alias.
- New DOM suites test_visibility_service.js and test_display_page.js;
  test_display_partial_ids.js imports the module.

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

* refactor(web): no computed keys in the Display page's readout and destroy

Codacy's object-injection rule flagged v[id] and ctx.state[name].

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

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

test/js/README.md

@@ -59,7 +59,7 @@ server has none.
 | `unit/test_page_registry.js` | no | The page lifecycle in `js/core/registry.js` (a minimal DOM shim): one `init` per `data-page` root, `destroy` and an aborted `ctx.signal` when htmx swaps it away, a vetoed swap keeps it, lazy page modules, a root removed without htmx swept on the next swap |
 | `unit/test_core_modules.js` | no | `js/core/api.js` (JSON envelope, HTTP/`status: error`/network errors, abort passthrough, the #683 login redirect, same-server paths only) and `js/core/facade.js` (`window.LEDMatrix`, deprecated aliases) |
 | `unit/test_overview_reconciliation_poll.js` | no | The Overview's reconciliation-banner poll from `partials/overview.html`, run in a vm: it gives up after a bounded number of requests when the status never says done, runs only while the Overview is on screen (`LEDVisibility`, its own key), and stops once the banner is shown |
-| `unit/test_display_partial_ids.js` | no | `partials/display.html`: every literal `getElementById()` in its inline scripts names an id the partial renders, and moving the brightness slider (the shipped script, in a vm with a fake DOM) updates its label without throwing |
+| `unit/test_display_partial_ids.js` | no | `js/pages/display.js` started on a fake root that answers only for the ids `partials/display.html` renders: every id it looks up (with every listener and timer it set fired) exists, and moving the brightness slider updates its label without throwing |
 | `unit/test_general_web_login_token.js` | no | `createToken` from `js/pages/general.js`, imported with a fake DOM and fetch: a created API token clears the form's `data-dirty` mark (so a reload does not ask "Leave site?"), a refused one keeps it |
 | `unit/test_plugin_action_delegation.js` | no | The document-level card-action delegation and `handlePluginAction` from `plugins_manager.js`, run with the handler inside an IIFE as in the real file: each action is handled once, a Starlark app uninstall goes to `DELETE /starlark/apps/<id>`, and an uninstall is confirmed once |
 | `dom/test_installed_dom.js` | yes | The toolbar in a real DOM: pill/search/sort interaction, the HTMX partial re-swap, and a `getComputedStyle` check that `.filter-pill[data-active]` really matches the emitted markup |
@@ -70,6 +70,8 @@ server has none.
 | `dom/test_operation_history_page.js` | yes | The Operation History tab (`js/pages/operation-history.js`): one request per swap and per Refresh, the plugin filter filled once, paging, filters, search, Clear, error/login states, hostile values stay text |
 | `dom/test_raw_json_page.js` | yes | The Config Editor tab (`js/pages/raw-json.js`): one POST per Save after repeated swaps, Format/Validate, invalid JSON never sent, a save survives a swap, the old global entry points |
 | `dom/test_schedule_page.js` | yes | The Schedule tab (`js/pages/schedule.js`) with the real `schedule-picker` widget: both pickers drawn once per swap from the saved config, one notification per save answer after repeated swaps, the brightness label, a late widget waited for, the old global entry points |
+| `dom/test_visibility_service.js` | yes (no server) | `js/core/visibility.js` with the real `LEDVisibility` from `app-shell.js` and the real registry: start/stop with the active tab and the browser tab's visibility, no interval while hidden or after a swap-out, registrations independent, the no-`LEDVisibility` fallback |
+| `dom/test_display_page.js` | yes | The Display tab (`js/pages/display.js`) with the real `plugin-order-list` widget and `LEDVisibility`: one page, one sync interval and one action per control after repeated swaps, the sync poll only while on screen and never after a swap-out, sync states as text, the debounced scroll-speed hint, `updateSyncUI`'s entry point |
 | `dom/test_general_page.js` | yes | The General tab (`js/pages/general.js`) with the real `timezone-selector` widget: the picker drawn once per swap, one request per Security action after repeated swaps, hostile token names stay text, refused/network/login answers, a write survives a swap, `webLogin`'s entry points |
 | `dom/test_backup_restore_page.js` | yes | The Backup & Restore tab (`js/pages/backup-restore.js`): one request per action after repeated swaps, the upload and restore options, reads cancelled and writes not on a swap, hostile names stay text, the old global entry points |
 | `dom/test_tools_sections.js` | yes | The Tools tab's MQTT bridge and Pixlet editor sections: form prefill, the write-only password (blank means unchanged), the running-session banner and countdown, and that the editor link points at the host you loaded the page from |