task(F4): library providers - builtin catalogs (event/architecture/landscape 15 blocks each), user-library and global-library via LibraryProviderExtension, panel UI with existing Drop-Channel

frontend/src/styles.css

@@ -2796,3 +2796,42 @@ body.drawer-open { overflow: hidden; }
   background: var(--color-accent);
   opacity: 0.7;
 }
+
+
+/* ─── Task F4 – LibraryProviderPanel ─── */
+.lib-provider-panel {
+  display: flex;
+  flex-direction: column;
+  gap: 8px;
+  padding: 8px 0 4px;
+  border-top: 1px solid rgba(255, 255, 255, 0.08);
+}
+.lprov-section { display: flex; flex-direction: column; gap: 4px; }
+.lprov-title {
+  font-size: 11px;
+  font-weight: 600;
+  color: #9aa0a6;
+  text-transform: uppercase;
+  letter-spacing: 0.04em;
+  padding: 2px 8px;
+}
+.lprov-grid {
+  display: grid;
+  grid-template-columns: repeat(auto-fill, minmax(56px, 1fr));
+  gap: 6px;
+  padding: 0 8px;
+}
+.lprov-block {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  padding: 6px 4px;
+  background: transparent;
+  border: 1px solid transparent;
+  border-radius: 6px;
+  cursor: grab;
+  color: inherit;
+  min-height: 44px;
+}
+.lprov-block:hover { background: rgba(255, 255, 255, 0.06); border-color: rgba(255, 255, 255, 0.12); }
+.lprov-block .tree-thumb svg { width: 44px; height: 36px; display: block; }