pi session context persistence, fix new session button, add clear all sessions

- handle pi process death by nulling piProcess ref so next message respawns
- replay conversation history on respawn via --session flag
- fix user message JSONL format to array for pi compatibility
- fix container sessions mount to match storage path
- fix ChatPanelWrapper: key on inner component so usePiChat resets on new session
- add bulk delete sessions endpoint and clear all button in chat header

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

src/workspaces/state/src/useChatSessions.ts

@@ -46,6 +46,14 @@ export function useChatSessions(filter?: ChatSessionsFilter) {
     );
   }
 
+  async function clearSessions() {
+    await client.delete('/pi/sessions', {
+      ...(filter?.context ? { context: filter.context } : {}),
+      ...(filter?.contextId ? { contextId: filter.contextId } : {}),
+    });
+    queryClient.setQueryData<SessionEntry[]>(['PI_SESSIONS', filter?.context, filter?.contextId], []);
+  }
+
   function searchSessions(query: string) {
     return client.get<{ results: SessionEntry[] }>(`/pi/sessions/search?q=${encodeURIComponent(query)}`);
   }
@@ -60,6 +68,7 @@ export function useChatSessions(filter?: ChatSessionsFilter) {
     saveMessages,
     renameSession,
     deleteSession,
+    clearSessions,
     searchSessions,
     invalidate,
   };