fix(sessions): stabilize setAllSessions to prevent polling loop

Wrap setAllSessions in useCallback so it has a stable reference.
This breaks the infinite re-render loop that was causing 4-10
requests per second to /users/me/sessions.

apps/web/src/state/sessions.tsx

@@ -1,4 +1,4 @@
-import { createContext, useContext, useState, type ReactNode } from "react";
+import { createContext, useCallback, useContext, useState, type ReactNode } from "react";
 
 export interface Session {
   id: string;
@@ -24,9 +24,9 @@ const SessionsContext = createContext<SessionsContextType | undefined>(undefined
 export const SessionsProvider = ({ children }: { children: ReactNode }) => {
   const [sessions, setSessions] = useState<Session[]>([]);
 
-  const setAllSessions = (newSessions: Session[]) => {
+  const setAllSessions = useCallback((newSessions: Session[]) => {
     setSessions(newSessions);
-  };
+  }, []);
 
   return (
     <SessionsContext.Provider value={{ sessions, setAllSessions }}>