navigation: one glass bar for the app's life, not one per page

The bar was rendered by each view, so `<CurrentView />` swapping on every
navigation destroyed it and built a new one. Measured: the `.glassbar`
element is not the same node on either side of an artist -> album move, and
the old one is disconnected.

That broke the crumb entrance animation, which is what this was noticed
from. The `seen` set exists so only a genuinely ARRIVING crumb slides in,
and it is component state -- so it was empty on every mount and every crumb
looked new. Instrumenting Element.animate across one navigation:

  AC/DC -> Highway to Hell   should animate: the album
                             actually animated: all three crumbs
  Back to AC/DC              should animate: nothing
                             actually animated: both crumbs

So the whole trail re-flew in from the right on every page change, and Back
animated crumbs that had never left -- the exact opposite of the
direction-of-travel cue the animation was written for.

The bar is app chrome, not part of a page, so App.svelte now mounts it once
as the scroll pane's first child and pages no longer carry it. Views that
do not show it yet hide it with `display: none` rather than an {#if}: the
element leaves the layout and measures zero -- scrollbar.js reads this
bar's height to start the thumb below it, and correctly gets 0 -- while the
component stays alive and keeps its crumb memory across the round trip.

Geometry is unchanged, which the negative-margin bleed made easy to get
wrong: the bar's net flow height is zero either way, so moving it from
first-child-of-the-page to previous-sibling-of-the-page leaves the page's
top exactly where it was. Verified against the live pane -- bar top/left/
width flush with the pane and 46 high, page top at pane + 24, z-index 40
and elementFromPoint at the bar's centre still returning the bar rather
than the hero underneath.

After: arriving at an album animates only the album's own crumb, Back
animates nothing, and a trip out to Library and back animates nothing. The
backdrop-filter layer is no longer recomposited on every page change, and a
bar element can now transition between pages at all, which was impossible
when each side was a different node.

Two consequences worth stating. The resolver pulse takes the GLOBAL accent
everywhere now; on the album page it used to inherit that page's extracted
palette, because the bar sat inside `.album-page`. The artist page always
gave it the global accent, so the two now agree rather than disagreeing.
And putting the bar on the remaining pages is now widening BAR_VIEWS plus
deciding how it sits against each page's existing header -- the mounting
question is settled.

85 JS tests pass.

src/views/CatalogAlbum.svelte

@@ -29,7 +29,6 @@
     import { listenerHeat, listenerPeak, listenerShare } from "../lib/listenerBars.js";
     import { consumeScroll, restoreScroll } from "../lib/navigation.svelte.js";
     import Icon from "../components/Icon.svelte";
-    import GlassBar from "../components/GlassBar.svelte";
 
     const page = $derived(catalog.albumPage); // { album, tracks, album_plays, … }
     const album = $derived(page?.album ?? null);
@@ -509,8 +508,6 @@
 </script>
 
 <div class="album-page" style={accentStyle} bind:this={pageEl}>
-    <GlassBar />
-
     {#if catalog.albumLoading}
         <p class="hint">Loading album…</p>
     {:else if !page}

src/views/CatalogArtist.svelte

@@ -44,7 +44,6 @@
     import { openPreview } from "../lib/preview/previewSession.svelte.js";
     import { traceToSvg, svgDataUrl } from "../lib/trace.js";
     import Icon from "../components/Icon.svelte";
-    import GlassBar from "../components/GlassBar.svelte";
     import { consumeScroll, restoreScroll } from "../lib/navigation.svelte.js";
     import HeroGpuCanvas from "../components/HeroGpuCanvas.svelte";
 
@@ -4459,10 +4458,11 @@
             </div>
         </div>
 
-        <!-- The shared frosted header (src/components/GlassBar.svelte); it
-             floats over the seam tail's mirror at the top. Its -24px margin is
-             what the pin geometry below is measured against. -->
-        <GlassBar />
+        <!-- The shared frosted header (src/components/GlassBar.svelte) floats
+             over the seam tail's mirror at the top. It is mounted by App.svelte
+             as the scroll pane's first child, not here — but its -24px bleed is
+             still what the pin geometry below is measured against, and its net
+             flow height is zero either way, so this spacer's top is unmoved. -->
 
         <!-- Pure spacer now: it still reserves the room the artwork needs and
              still sets where the content begins (both from its aspect-ratio,