feat: redesign sidebar with richer session cards and visual polish

- Session cards now show orchestration mode icon (colored per type:
  indigo=single, amber=sequential, emerald=concurrent, sky=handoff,
  violet=group-chat) giving at-a-glance pattern visibility
- Add relative timestamps (just now, 2m ago, yesterday, etc.)
- Running sessions show animated pulse on left accent bar and
  text status label instead of static dot
- Multi-agent sessions display agent count badge (Users icon + count)
- Error sessions show explicit red Error label
- Project headers show running session count as live badge
  and total count as pill; folder icon highlights on hover
- Upgrade Kopaya logo from letter badge to gradient icon with
  Sparkles, add BETA tag
- Move New Session button to prominent dashed-border CTA below header
- Better empty state with composite folder+plus icon treatment
  and indigo Add Project button
- Add sidebar-pulse CSS keyframe animation for running indicators

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/renderer/styles.css

@@ -103,6 +103,16 @@ textarea {
   max-height: 200px;
 }
 
+/* Sidebar running-session pulse animation */
+@keyframes sidebar-pulse {
+  0%, 100% { opacity: 1; }
+  50% { opacity: 0.4; }
+}
+
+.sidebar-pulse {
+  animation: sidebar-pulse 2s ease-in-out infinite;
+}
+
 /* Markdown prose styles for chat messages */
 .markdown-content {
   line-height: 1.7;