fix(spa): bare-channel create reachable on an empty lineup (#212 reopened)

ChannelsScreen returned ChannelsEmptyState before the action bar that owns
"New blank channel", so a fresh install could never create its first channel.
The empty state now offers both create paths (bare-create + ChannelBuilder),
reusing the exact createBlankChannel handler (number = max+1 → 1 on empty,
group "ErsatzTV", default ffmpeg profile).

Regression: App.test.tsx bare-creates from a [] lineup, asserts the POST
payload (number "1") + navigation to /app/edit-channel/{id}.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

web/src/shell.css

@@ -1275,6 +1275,21 @@ body {
   font-size: var(--text-sm, 13px);
 }
 
+.ctv-channels-empty {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  gap: 16px;
+  padding: 16px 0;
+}
+
+.ctv-channels-empty-actions {
+  display: flex;
+  gap: 10px;
+  flex-wrap: wrap;
+  justify-content: center;
+}
+
 .ctv-schedule-inspector {
   display: flex;
   flex-direction: column;