feat(ui): double showcase cadence + filter bar matches TopNav frost

- Showcase reveal cadence 80ms -> 160ms (slower, more deliberate one-at-a-time
  cascade per operator). Bump showcase.spec timer advances to cover 60x160ms.
- Gallery filter bar now uses the EXACT gradiated-obsidian frost + blur as
  TopNav (was a flat rgba(...,0.55) block), so the two read as one continuous
  piece of chrome with images visibly scrolling under both; the nav's
  transparent bottom edge against the bar's opaque top leaves a faint seam that
  separates them at the very top of scroll.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/components/gallery/GalleryFilterBar.vue

@@ -217,7 +217,7 @@ function pushFilter(mutate) {
 
 <style scoped>
 /* The whole chrome (bar row + expandable refine panel) is one sticky,
-   hazey block pinned directly under the 64px TopNav and continuous with it. */
+   frosted block pinned directly under the 64px TopNav and continuous with it. */
 .fc-filterbar-wrap {
   position: sticky;
   top: 64px;
@@ -227,9 +227,18 @@ function pushFilter(mutate) {
      and a gap shows through when scrolled to the top. */
   margin-top: -8px;
   margin-bottom: 12px;
-  /* Same hazey obsidian (#14171A = 20,23,26) + blur as the TopNav so the two
-     read as one piece of chrome; content scrolls under both. */
-  background: rgba(20, 23, 26, 0.55);
+  /* EXACT same gradiated obsidian (#14171A = 20,23,26) frost as the TopNav so
+     the two read as one continuous piece of chrome — images scroll visibly
+     under both. The nav's gradient fades to transparent at ITS bottom; this
+     bar re-darkens at its top, so a faint seam (the page/image showing through
+     the nav's transparent edge) separates them when scrolled to the very top,
+     while under-scroll they frost as one. */
+  background: linear-gradient(
+    to bottom,
+    rgba(20, 23, 26, 0.92) 0%,
+    rgba(20, 23, 26, 0.65) 60%,
+    rgba(20, 23, 26, 0) 100%
+  );
   backdrop-filter: blur(2px);
   -webkit-backdrop-filter: blur(2px);
 }

frontend/src/stores/showcase.js

@@ -24,7 +24,8 @@ import { preloadImage } from '../utils/preloadImage.js'
 // fetch + decode (a cold TABLESAMPLE is a separate, query-side concern);
 // everything after it is buffer-smoothed.
 const PAGE = 3
-const CADENCE_MS = 80          // floor between fully-loaded reveals
+const CADENCE_MS = 160         // floor between fully-loaded reveals (doubled
+                              // 2026-06-04 — slower, more deliberate cadence)
 const PRIME = 6                // items buffered before the drain starts
 const BUFFER_TARGET = 30       // producer tops the queue up to this
 const BUFFER_MIN = 12          // ...and refills once the queue dips below this

frontend/test/showcase.spec.js

@@ -46,8 +46,8 @@ describe('showcase store: buffered cascade', () => {
     stubShowcase()
     const s = useShowcaseStore()
     const p = s.loadInitial()
-    // Past INITIAL_COUNT (60) × CADENCE (80ms) plus fetch microtasks.
-    await vi.advanceTimersByTimeAsync(6000)
+    // Past INITIAL_COUNT (60) × CADENCE (160ms = 9.6s) plus fetch microtasks.
+    await vi.advanceTimersByTimeAsync(12000)
     await p
     expect(s.images.length).toBe(60)
     const ids = s.images.map((i) => i.id)
@@ -65,7 +65,7 @@ describe('showcase store: buffered cascade', () => {
     // the cadence — a 1s window must not dump the whole buffer at once.
     expect(early).toBeGreaterThan(0)
     expect(early).toBeLessThan(60)
-    await vi.advanceTimersByTimeAsync(6000)
+    await vi.advanceTimersByTimeAsync(12000)
     await p
     expect(s.images.length).toBe(60)
   })
@@ -80,7 +80,7 @@ describe('showcase store: buffered cascade', () => {
     await vi.advanceTimersByTimeAsync(1000)
     expect(s.images.length).toBe(0)   // gated on the un-decoded first image
     release()
-    await vi.advanceTimersByTimeAsync(6000)
+    await vi.advanceTimersByTimeAsync(12000)
     await p
     expect(s.images.length).toBe(60)  // cascade proceeds once it decodes
   })