Complete frontend migration to unified Pi harness (Phase 7 + Phase 9)

- Delete legacy hooks: useClaude.ts, useOpenCode.ts, usePiMono.ts, App.backup.tsx
- Update all components to use usePi instead of legacy hooks
- Replace useVisiblePiMonoModels/useClaudeModels/useOpenCodeModels with useVisiblePiModels
- Migrate from LegacyChatMessage to ChatMessage type throughout
- Update SessionBar to remove provider and archive props
- Simplify ChatDetailPanel to Pi-only (remove Claude/OpenCode components)
- Fix useChatSessions calls (remove provider parameter)
- Update user-settings types: provider now only 'pi' instead of legacy values
- Update PI_HARNESS_REBUILD.md to mark phases complete

src/apps/officer-web/Screens/Dashboard/Files/Screen/TaskRunnerModal.tsx

@@ -4,9 +4,9 @@ import { Dialog, DialogOverlay, DialogPortal } from '@/components/ui/dialog';
 import * as DialogPrimitive from '@radix-ui/react-dialog';
 import { cardStyle } from '@/components/Card';
 import type { TaskInfo } from 'apps/Chat';
-import { usePiMono } from '@/Screens/Dashboard/Chat/usePiMono';
+import { usePi } from '@/Screens/Dashboard/Chat/usePi';
 import { EmbeddableChat } from '@/Screens/Dashboard/Chat/EmbeddableChat';
-import { useVisiblePiMonoModels } from '@/state/useModels';
+import { useVisiblePiModels } from '@/state/useModels';
 import { useSettings } from '@/state/useSettings';
 import type { TaskSummary } from 'apps/FileBrowser';
 
@@ -47,8 +47,8 @@ const PiMonoInner = ({
   initialModel,
   taskInfo,
 }: PiMonoInnerProps) => {
-  const chat = usePiMono(undefined, initialModel, { replaceUrl: false, taskInfo });
-  const models = useVisiblePiMonoModels();
+  const chat = usePi(undefined, initialModel, { replaceUrl: false, taskInfo });
+  const models = useVisiblePiModels();
 
   const wasGenerating = useRef(false);
   useEffect(() => {
@@ -108,10 +108,10 @@ export const TaskRunnerModal = ({ open, onOpenChange, task, entryName, entryType
 
           {/* Chat */}
           <PiMonoInner
-            key="pi-mono"
+            key="pi"
             defaultInput={defaultInput}
             cwd={cwd}
-            initialModel={taskSettings.defaultProvider === 'pi-mono' ? taskSettings.defaultModel : null}
+            initialModel={taskSettings.defaultProvider === 'pi' ? taskSettings.defaultModel : null}
             taskInfo={taskInfo}
           />
         </DialogPrimitive.Content>