saved sessions: replace transient history with persistent DB storage and auto-save

- Add saved_sessions table and CRUD endpoints (save, list, resume, update, delete)
- Save is instant (no LLM summarization), stores exact conversation with tool calls
- Resume loads full message history into chat UI, sends transcript to agent on first message
- Auto-save updates DB after every agent response once a session is saved
- Delete old filesystem-based session/group management (sessions router, useChatSessions, useChatGroups)
- Clean up ChatHeader, SessionList, ChatDetailPanel for saved sessions flow

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/apps/officer-web/Screens/Dashboard/ChatHistory/index.tsx

@@ -5,7 +5,6 @@ import { WorkspaceView } from 'officerdev';
 import { useIsMobile } from 'hooks/useIsMobile';
 import { useDashboardState } from 'state/useDashboardState';
 import { usePanelChannel } from 'hooks/usePanelChannel';
-import { useChatSessions } from 'state/useChatSessions';
 import { defaultLayout } from './defaultLayout';
 
 export { ChatHistory as ChatHistoryApp } from './Widget';
@@ -35,7 +34,6 @@ type SessionListPageProps = {
 
 export const SessionListPage = ({ isNew }: SessionListPageProps) => {
   const { sessionId } = useParams<{ sessionId: string }>();
-  const { sessions } = useChatSessions();
   const [, setSelected] = usePanelChannel<SelectedSession>('chat:selected-session', null);
   const rawWorkspace = useDashboardState<LayoutNode>('screens/chat', defaultLayout);
   const isMobile = useIsMobile();
@@ -62,8 +60,7 @@ export const SessionListPage = ({ isNew }: SessionListPageProps) => {
       return;
     }
     if (!sessionId) return;
-    const session = sessions.find((s) => s.id === sessionId);
-    setSelected({ id: sessionId, model: session?.model ?? null });
+    setSelected({ id: sessionId });
   }, [sessionId, isNew]);
 
   return (