refactor(state): clean layoutStore, add selectors, centralise STALE constants

- layoutStore: remove 4 dead field groups (pinnedPanels, selectedResultId,
  compareTrayVisible, notificationsOpen) — none were read outside the store
- CompareTray: drop dead useLayoutStore side-effect (state was write-only)
- 8 components: replace bare useStore() with explicit selectors / useShallow
  to prevent unnecessary re-renders on unrelated state mutations
- lib/constants: add STALE_MARKET_SIGNALS + STALE_REVIEW_QUEUE (30s each)
- useMarketSignals, useReviewQueue: use global constants instead of
  hook-local magic numbers
- Add STATE_MANAGEMENT.md: decision tree + rules for RQ/Zustand/local/derived

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

src/provider/AuthProvider.tsx

@@ -16,7 +16,10 @@ interface AuthContextValue {
 const AuthContext = createContext<AuthContextValue | null>(null)
 
 export function AuthProvider({ children }: { children: ReactNode }) {
-  const { currentUser, isAuthenticated, login, logout } = useSessionStore()
+  const currentUser = useSessionStore(s => s.currentUser)
+  const isAuthenticated = useSessionStore(s => s.isAuthenticated)
+  const login = useSessionStore(s => s.login)
+  const logout = useSessionStore(s => s.logout)
 
   const value: AuthContextValue = {
     user: currentUser,