feat(queue): give an overlaid queue a place in the back stack

The queue's pixels were already right. Measured at the reference
device's 424x439, #24's overlay is 424x318 -- `.main-panel`'s rect
exactly -- so the `DETAIL_LOADERS` mount the issue's Direction asks for
would draw the same rectangle in the same place. What was missing was
the navigation model: opening the queue on Artists and pressing back
moved the page *underneath* to Albums and left the queue up, which is a
press that changes something the user cannot see and costs them their
place.

So the queue is a *place* exactly while it is an overlay, and a
*control* while it is a column. A column is a thing the user docked --
back must not undock it and a navigation must not take it away -- and
that reuses #24's computed mode rather than adding a breakpoint, so the
drag-resizable panel width keeps deciding it.

It is in neither `VIEW_TAGS` nor `DETAIL_LOADERS`, because there is
nothing to mount and moving it would cost something. `.main-panel > *`
computes `contain: content` under a `.main-panel` that does too, and
paint containment clips the `position: fixed` a `wa-popup` falls back
to on Chrome 113 (#60) -- so the detail-view mount would have broken
`queue-panel`'s working context menu on the one device this is about.
The panel's ancestry today is paint-free to `body`.

Two details that fail silently otherwise. The entry is unwound from the
panel's `open` attribute in the observer that already ran for
`aria-expanded`, not at each of the four ways out -- without that the
entry is orphaned and the *next* back press is the one that closes the
queue, which is this defect moved one press later. And the navigation
writes neither `dataset.activeView` nor `searchStore.setCurrentView`,
because both describe what is *in* the main panel and the queue covers
that panel without replacing it.

`now-playing-view`'s copy of the button went through the helper too: it
set `open` directly, so on a phone it produced exactly the queue with no
entry behind it that this removes.

Closes #55

frontend/src/components/now-playing-view/now-playing-view.ts

@@ -15,6 +15,7 @@ import { FavoritesController } from '@store/controllers/favorites-controller';
 import { designTokens } from '../../styles/tokens.css';
 import { srOnly } from '../../styles/sr-only.css';
 import { ICON_QUEUE } from '@utils/icon-language';
+import { openQueue as showQueue } from '@utils/open-queue';
 
 /**
  * What is playing, at the size a phone has room for (plan 016 B2,
@@ -226,13 +227,15 @@ export class NowPlayingView extends LitElement {
      *
      * This view hides the bottom bar (index.css), and the bar is where
      * the queue button lives -- so without this, going full-screen
-     * would take the queue away. It toggles the same `open` attribute
+     * would take the queue away. It goes through the same helper
      * `index.ts` does, because the panel's state is an attribute on one
      * element and a second mechanism for it is a second thing to keep
-     * in step.
+     * in step -- which is exactly what this button was: it set `open`
+     * directly, so on a phone it produced a queue with no history entry
+     * behind it and back moved the page underneath instead (#55).
      */
     private openQueue() {
-        document.getElementById('queue-panel')?.setAttribute('open', '');
+        showQueue();
     }
 
     private toggleFavorite() {