Enhance session sidebar with PR worktree support (#342)

* feat: refactored sessions sidebar to be workspaces centric

- Add createWorktreeOnly helper and status checks
- Add createWorktreeOnly to create a standalone worktree for the active project
- Show error toasts when no active project or not a Git repository
- Refresh session list and show success toast with created worktree details

* feat: show attention indicator and status marker in SessionSidebar

- Show unread attention indicator for sessions with pending updates
- Display status marker combining streaming and unread indicators in the session row
- Introduce attention diamond pulse animation and associated CSS for the new indicator

* fix(SessionSidebar): reserve header actions space when repo state is known

* chore(doc): add PR status colors to custom themes

packages/ui/src/index.css

@@ -802,6 +802,19 @@ textarea[data-terminal-hidden-input="true"]::placeholder {
   animation: grid-pulse 1.2s ease-in-out infinite;
 }
 
+@keyframes attention-diamond-pulse {
+  0%, 100% {
+    opacity: 0.52;
+  }
+  50% {
+    opacity: 0.92;
+  }
+}
+
+.animate-attention-diamond-pulse {
+  animation: attention-diamond-pulse 2.3s ease-in-out infinite;
+}
+
 @keyframes marquee-scroll {
   0% { transform: translateX(0); }
   100% { transform: translateX(-100%); }
@@ -828,4 +841,9 @@ textarea[data-terminal-hidden-input="true"]::placeholder {
   .marquee-text--active:hover {
     animation: none;
   }
+
+  .animate-grid-pulse,
+  .animate-attention-diamond-pulse {
+    animation: none;
+  }
 }