PALETTE: swatch preview + tooltip + OK commit — TDD

Clicking a swatch instantly swaps the body palette class for a live
preview; OK commits silently (POST, no reload); click-elsewhere or
10 s auto-dismiss reverts. Tooltip portal shows label, shoptalk,
lock state. Locked swatches show × (disabled). 20 FTs green.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/static_src/scss/_dashboard.scss

@@ -66,7 +66,8 @@ body.page-dashboard {
 
         .palette-scroll {
             display: flex;
-            gap: 3.5rem;
+            gap: 1rem;
+            align-items: center;
             overflow-x: auto;
             padding: 0.75rem 2rem;
             height: 100%;