Snapshot URL datasets locally on add; preview tabular data as a table

src/app/components/DatasetsModal.module.css

@@ -235,6 +235,32 @@
   color: var(--text-secondary);
 }
 
+/* URL dataset provenance: the source address + last-fetched time (spec §05). */
+.sourceMeta {
+  display: flex;
+  flex-wrap: wrap;
+  align-items: baseline;
+  gap: var(--space-2) var(--space-4);
+  margin: 0;
+  font-size: 12px;
+  color: var(--text-secondary);
+}
+
+.sourceLink {
+  color: var(--accent);
+  text-decoration: none;
+  overflow-wrap: anywhere;
+}
+
+.sourceLink:hover {
+  text-decoration: underline;
+}
+
+.sourceLink:focus-visible {
+  outline: 2px solid var(--focus);
+  outline-offset: 2px;
+}
+
 .section {
   display: flex;
   flex-direction: column;
@@ -335,6 +361,46 @@
   white-space: pre;
 }
 
+/* Tabular preview — a scrollable grid with a sticky header (spec §05 → Preview). */
+.previewTableWrap {
+  max-height: 260px;
+  overflow: auto;
+  border: var(--border-width) solid var(--border);
+  border-radius: var(--radius);
+}
+
+.previewTable {
+  border-collapse: collapse;
+  width: 100%;
+  font-family: var(--font-mono);
+  font-size: 12px;
+  line-height: 1.4;
+}
+
+.previewTable th,
+.previewTable td {
+  text-align: left;
+  padding: var(--space-2) var(--space-3);
+  border-bottom: var(--border-width) solid var(--border);
+  white-space: nowrap;
+  max-width: 240px;
+  overflow: hidden;
+  text-overflow: ellipsis;
+}
+
+.previewTable thead th {
+  position: sticky;
+  top: 0;
+  z-index: 1;
+  background: var(--layer-01);
+  font-weight: 600;
+  color: var(--text-secondary);
+}
+
+.previewTable tbody tr:last-child td {
+  border-bottom: none;
+}
+
 .muted {
   margin: 0;
   font-size: 13px;
@@ -439,3 +505,10 @@
   font-size: 13px;
   color: var(--support-error);
 }
+
+/* The inline-fallback recovery under a failed URL fetch — left-aligned, not
+   stretched, so it reads as a secondary recovery beneath the error message. */
+.fallback {
+  align-self: flex-start;
+  margin-top: calc(-1 * var(--space-2));
+}