feat(web): move candidates/system nav to topbar, free mobile bottom nav

reaction_board/web/static/style.css

@@ -123,10 +123,30 @@ h1, h2, h3, p { margin: 0; }
   color: var(--muted);
   font-size: 11px;
 }
+.topbar-actions { display: flex; align-items: center; gap: 8px; flex: 0 0 auto; }
+.topbar-links { display: flex; align-items: center; gap: 6px; }
+.topbar-links a {
+  padding: 4px 10px;
+  border: 1px solid var(--border);
+  border-radius: 999px;
+  color: var(--muted);
+  font-size: 11px;
+  white-space: nowrap;
+}
+.topbar-links a:hover {
+  color: var(--accent);
+  border-color: color-mix(in srgb, var(--accent) 55%, var(--border));
+}
+.topbar-links a.active {
+  color: var(--accent);
+  background: var(--accent-soft);
+  border-color: transparent;
+}
 .sidebar-topbar {
   display: none;
-  flex-direction: column;
-  align-items: flex-start;
+  flex-direction: row;
+  align-items: center;
+  justify-content: space-between;
   gap: 8px;
   width: 100%;
   padding: 0 4px 12px;