feat(chats): add managed projectless chat sessions

Create projectless chat sessions under a managed, date-scoped Chats directory and clean abandoned or deleted session folders.

Add Chats to sidebar state, startup cache, shared context, and Electron Mini Chat while keeping VS Code project-only. Resolve managed chat directories to one server-side memory owner and document the runtime contracts.

packages/web/server/index.js

@@ -1291,6 +1291,7 @@ const resolveMemoryProjectId = createMemoryProjectResolver({
     return sanitizeProjects(settings?.projects || []).map((project) => project.path);
   },
   resolvePrimaryWorktreeRoot,
+  managedProjectRoots: [path.join(OPENCHAMBER_USER_CONFIG_ROOT, 'chats')],
 });
 
 /**