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/components/layout/CompareTray.tsx

@@ -1,9 +1,7 @@
-import { useEffect } from 'react'
 import { useNavigate, useLocation } from 'react-router'
 import { Box, Button, IconButton, Typography } from '@mui/material'
 import { X } from 'lucide-react'
 import { useCompareStore } from '../../stores/compareStore'
-import { useLayoutStore } from '../../stores/layoutStore'
 
 const TYPE_DOT: Record<string, string> = {
   VERIFIED_PORTFOLIO:  '#1e3a5f',
@@ -14,15 +12,10 @@ const TYPE_DOT: Record<string, string> = {
 
 export function CompareTray() {
   const { compareItems, removeFromCompare, clearCompare } = useCompareStore()
-  const { setCompareTrayVisible } = useLayoutStore()
   const navigate = useNavigate()
   const location = useLocation()
   const isDemand = location.pathname.startsWith('/demand')
 
-  useEffect(() => {
-    setCompareTrayVisible(compareItems.length > 0 && isDemand)
-  }, [compareItems.length, setCompareTrayVisible, isDemand])
-
   if (!isDemand) return null
 
   const getTitle = (item: (typeof compareItems)[number]) => {