fix(artists): card preview dead-space + empty-state flicker on first load

Two operator-reported Artists-view bugs.

Layout: ArtistCard previews used aspect-ratio: 3/1 + max-height: 220px — when a
lone grid column got wide (>~660px), the max-height made the aspect-ratio box
shrink its own WIDTH to keep the ratio, leaving dead space beside the 3
thumbnails. Dropped max-height (kept the min-height floor) so the strip fills the
card width; lowered the grid min 440→360px so a lone column stays <732px (strip
≲244px) and desktop gets 2+ columns.

Flicker: isEmpty checked !loading, but on the first render loading is still false
(the initial loadMore fires in onMounted, after paint) so "No artists match"
flashed for a frame before the spinner/data. Added a reactive `loaded` flag (true
after the first load attempt, reset on reset()); isEmpty now also requires it.

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

frontend/src/stores/artistDirectory.js

@@ -14,6 +14,10 @@ export const useArtistDirectoryStore = defineStore('artistDirectory', () => {
   const q = ref('')
   const platform = ref(null)
   let started = false
+  // Has a load ATTEMPT completed yet? Gates the "No artists match" empty state
+  // so it can't flash on the very first render (loading is still false before
+  // onMounted fires the first loadMore) or between a query change and its fetch.
+  const loaded = ref(false)
   // Typed "alice" then "alice bob" used to drop the second fetch
   // entirely (loading flag still true from the first), so the UI
   // showed alice results while the input said "alice bob". Inflight
@@ -35,6 +39,7 @@ export const useArtistDirectoryStore = defineStore('artistDirectory', () => {
       nextCursor.value = body.next_cursor
       started = true
     })
+    if (t.isCurrent()) loaded.value = true
   }
 
   async function reset() {
@@ -42,6 +47,7 @@ export const useArtistDirectoryStore = defineStore('artistDirectory', () => {
     cards.value = []
     nextCursor.value = null
     started = false
+    loaded.value = false
     await loadMore()
   }
 
@@ -50,7 +56,8 @@ export const useArtistDirectoryStore = defineStore('artistDirectory', () => {
 
   const hasMore = computed(() => !started || nextCursor.value !== null)
   const isEmpty = computed(
-    () => !loading.value && cards.value.length === 0 && error.value === null
+    () => loaded.value && !loading.value
+      && cards.value.length === 0 && error.value === null
   )
 
   return {