Drop the redundant source column in the artifact list when a source is selected

When a single source is selected, every row in the middle sidebar repeats
that same source, so the source column is pure waste — the pane header
already names the source. The column now only shows under "All sources"
(where it's needed to tell rows apart); selecting a source hides it and
gives the width back to the artifact title. Also drops the now-dangling
row-main border-right in that state.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

static/daybook.css

@@ -556,6 +556,21 @@ h1 {
   padding: 0;
 }
 
+/* When a single source is selected, the per-row source column is redundant
+   (every row has the same source), so drop it and give the space back to the
+   title. Shown only under "All sources". */
+.artifact-list.no-source-col .artifact-row {
+  grid-template-columns: 3.15rem minmax(0, 1fr);
+}
+
+.artifact-list.no-source-col .artifact-source {
+  display: none;
+}
+
+.artifact-list.no-source-col .artifact-row-main {
+  border-right: 0;
+}
+
 .artifact-row:hover {
   background: var(--row-hover);
   box-shadow: none;

templates/artifacts/feed.html

@@ -53,7 +53,7 @@
         <span>{{ artifacts|length }} artifact{{ artifacts|length|pluralize }}</span>
       </div>
 
-      <div class="artifact-list" data-artifact-list>
+      <div class="artifact-list{% if selected_source %} no-source-col{% endif %}" data-artifact-list>
         {% if day_groups %}
           {% include "artifacts/_day_groups.html" with has_more=older_count next_before=window_start|date:"Y-m-d" %}
         {% else %}