stats banner: blue info variant when backfill is in progress

Existing yellow banner only fires for !ok (indexer stalled) or
skippedCount>0. With the caughtUp short-circuit added today, an actively-
backfilling indexer reports ok:true even when 100k+ blocks are still
being processed -- so the page rendered no signal at all despite
historical charts being incomplete.

Adds a third banner condition: ok && pendingCount > 0 renders a blue
info-style 'Backfill in progress' notice with the pending count and
current rate. Stylistically distinct from the yellow alert banners so
users can tell 'still working' apart from 'something's wrong.'

Author: hans-crypto

frontend/src/app/components/_ordpool/ordpool-stats/ordpool-stats.component.html

@@ -22,6 +22,18 @@
         </div>
       }
     </div>
+  } @else if (progress.pendingCount > 0) {
+    <div class="ordpool-status-banner ordpool-status-banner-info mb-3" role="status">
+      <div>
+        <strong>Backfill in progress.</strong>
+        {{ progress.pendingCount | number }} older
+        {{ progress.pendingCount === 1 ? 'block is' : 'blocks are' }} still being indexed.
+        @if (progress.blocksPerMinute !== null && progress.blocksPerMinute > 0) {
+          About {{ progress.blocksPerMinute | number:'1.0-0' }} blocks per minute right now.
+        }
+        Live charts are accurate; long historical ranges will fill in as blocks complete.
+      </div>
+    </div>
   }
 }
 

frontend/src/app/components/_ordpool/ordpool-stats/ordpool-stats.component.scss

@@ -14,6 +14,16 @@
   }
 }
 
+.ordpool-status-banner-info {
+  background-color: rgba(80, 160, 220, 0.12);
+  border-color: rgba(80, 160, 220, 0.5);
+  color: #a8d2f0;
+
+  strong {
+    color: #6fb6e8;
+  }
+}
+
 .menu {
   flex-grow: 1;
   padding: 0 35px;