board: spinner during first load instead of "no cards found"

An empty board on first load blurting "no cards found" was alarming
on a board the user knew had cards. Track a cardsLoaded flag that
flips on the first /api/cards (meta or full) response — or on a
cached-cards hydration — and show a centred spinner placeholder
while it's still false. The "no cards found" copy only shows once
we've actually heard back and the set is genuinely empty.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

public/js/modules/board.js

@@ -587,9 +587,18 @@ export function renderBoard() {
         board.style.display = 'flex';
         board.style.alignItems = 'center';
         board.style.justifyContent = 'center';
-        board.innerHTML = `<div class="flex flex-col items-center text-center">
-            <i class="ph ph-cards text-4xl text-t-dim mb-4 block"></i>
-            <p class="font-pixel text-sm text-t-dim cursor-blink">no cards found</p></div>`;
+        // Distinguish "genuinely empty" from "haven't heard back yet".
+        // Blurting "no cards found" during the initial load is scary
+        // on boards the user knows aren't empty.
+        if (!state.cardsLoaded) {
+            board.innerHTML = `<div class="flex flex-col items-center text-center">
+                <i class="ph ph-circle-notch text-4xl text-t-dim mb-4 block card-spinner"></i>
+                <p class="font-pixel text-sm text-t-dim">loading…</p></div>`;
+        } else {
+            board.innerHTML = `<div class="flex flex-col items-center text-center">
+                <i class="ph ph-cards text-4xl text-t-dim mb-4 block"></i>
+                <p class="font-pixel text-sm text-t-dim cursor-blink">no cards found</p></div>`;
+        }
         const fc = $('footer-count');
         if (fc) fc.textContent = `0 cards · ${state.cards.length} total`;
         return;