refactor: simplify sidebar project sorting

Removes recent-project grouping from the sidebar project list
Keeps project ordering based on manual and default sort rules only
Reduces memoized session-derived state in the sidebar

packages/ui/src/components/session/SessionSidebar.tsx

@@ -1037,46 +1037,6 @@ export const SessionSidebar: React.FC<SessionSidebarProps> = ({
   const projectSortOrder = useSessionDisplayStore((state) => state.projectSortOrder);
   const manualProjectOrder = useProjectsStore((state) => state.manualProjectOrder);
 
-  const recentProjectIdsRef = React.useRef<Set<string>>(new Set());
-  const recentProjectIds = React.useMemo(() => {
-    const recentSessions = deriveRecentSessions(sessions);
-    const ids = new Set<string>();
-
-    if (recentSessions.length > 0) {
-      const pathToId = new Map<string, string>();
-      for (const project of normalizedProjects) {
-        if (project.normalizedPath) {
-          pathToId.set(project.normalizedPath, project.id);
-        }
-      }
-
-      for (const session of recentSessions) {
-        const directory = normalizePath((session as Session & { directory?: string | null }).directory ?? null);
-        if (directory) {
-          const projectId = pathToId.get(directory);
-          if (projectId) ids.add(projectId);
-        }
-      }
-    }
-
-    // Sessions update on every SSE event; keep the previous Set reference when
-    // membership is unchanged so sortedProjects (and the sidebar sections built
-    // from it) do not recompute on every streaming event.
-    const previous = recentProjectIdsRef.current;
-    if (previous.size === ids.size) {
-      let unchanged = true;
-      for (const id of ids) {
-        if (!previous.has(id)) {
-          unchanged = false;
-          break;
-        }
-      }
-      if (unchanged) return previous;
-    }
-    recentProjectIdsRef.current = ids;
-    return ids;
-  }, [sessions, normalizedProjects]);
-
   const sortedProjects = React.useMemo(() => {
     const list = [...normalizedProjects];
 
@@ -1112,14 +1072,8 @@ export const SessionSidebar: React.FC<SessionSidebarProps> = ({
       }
     }
 
-    if (projectSortOrder === 'manual') {
-      return list;
-    }
-
-    const recent = list.filter((p) => recentProjectIds.has(p.id));
-    const rest = list.filter((p) => !recentProjectIds.has(p.id));
-    return [...recent, ...rest];
-  }, [normalizedProjects, projectSortOrder, manualProjectOrder, recentProjectIds]);
+    return list;
+  }, [normalizedProjects, projectSortOrder, manualProjectOrder]);
 
   const {
     projectSections,