feat(queue): add persistent download history with active/history tabs

Adds a downloads panel inside the resolve queue UI with two tabs:
- Active: live downloads
- History: completed or already-downloaded entries

History is persisted in localStorage (model_resolver_download_history, capped at 200 entries) via new helper methods on queueMethods. Downloads complete by calling rememberCompletedDownloadHistory(), which records filename, category, workflow, node, target path, size, status and timestamp. CSS additions cover the subtab bar, history item layout, and a small status badge.

web/css/resolver-shell.css

@@ -393,6 +393,16 @@
     font-size: 13px;
 }
 
+.mr-downloads-panel {
+    display: grid;
+    gap: 0;
+    min-height: 0;
+}
+
+.mr-downloads-subtabs {
+    margin: 0 0 -1px;
+}
+
 .mr-queue-items {
     display: flex;
     flex-direction: column;
@@ -495,6 +505,29 @@
     border-radius: 999px;
 }
 
+.mr-download-history-toolbar {
+    display: flex;
+    justify-content: flex-end;
+    padding: 0 8px 4px;
+}
+
+.mr-download-history-status {
+    flex: 0 0 auto;
+    max-width: 130px;
+    padding: 2px 6px;
+    overflow: hidden;
+    color: #d7d7d7;
+    font-size: 10px;
+    font-weight: 800;
+    line-height: 1.2;
+    text-overflow: ellipsis;
+    text-transform: uppercase;
+    white-space: nowrap;
+    background: rgba(255, 255, 255, 0.07);
+    border: 1px solid rgba(255, 255, 255, 0.105);
+    border-radius: 999px;
+}
+
 .mr-download-queue-progress {
     display: grid;
     gap: 4px;