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/hooks/useMarketSignals.ts

@@ -3,14 +3,13 @@ import { marketIntelligenceService } from '../services/marketIntelligenceService
 import { reviewService } from '../services/reviewService'
 import type { MarketSignalFilters, SignalProcessingStatus } from '../domain/marketSignal'
 import { useToastStore } from '../stores/toastStore'
-
-const STALE_SIGNALS = 30_000
+import { STALE_MARKET_SIGNALS } from '../lib/constants'
 
 export function useMarketSignals(filters?: MarketSignalFilters) {
   return useQuery({
     queryKey: ['market-signals', filters ?? {}],
     queryFn: () => marketIntelligenceService.getSignals(filters),
-    staleTime: STALE_SIGNALS,
+    staleTime: STALE_MARKET_SIGNALS,
     select: (res) => res.data ?? [],
   })
 }
@@ -20,7 +19,7 @@ export function useMarketSignalDetail(id: string | null) {
     queryKey: ['market-signal', id],
     queryFn: () => marketIntelligenceService.getSignalDetail(id!),
     enabled: id !== null,
-    staleTime: STALE_SIGNALS,
+    staleTime: STALE_MARKET_SIGNALS,
     select: (res) => res.data ?? null,
   })
 }

src/hooks/useReviewQueue.ts

@@ -4,15 +4,15 @@ import { useSessionStore } from '../stores/sessionStore'
 import type { ReviewFilters } from '../provider/IReviewProvider'
 import type { ReviewTaskStatus } from '../domain/review'
 import { useToastStore } from '../stores/toastStore'
+import { STALE_REVIEW_QUEUE } from '../lib/constants'
 
-const STALE_REVIEW = 30_000
 const QK = 'reviewQueue'
 
 export function useReviewQueue(filters?: ReviewFilters) {
   return useQuery({
     queryKey: [QK, filters ?? {}],
     queryFn: () => reviewService.getTasks(filters),
-    staleTime: STALE_REVIEW,
+    staleTime: STALE_REVIEW_QUEUE,
     select: (res) => res.data ?? [],
   })
 }
@@ -21,7 +21,7 @@ export function useReviewTask(id: string | null) {
   return useQuery({
     queryKey: [QK, 'task', id],
     queryFn: () => reviewService.getTask(id!),
-    staleTime: STALE_REVIEW,
+    staleTime: STALE_REVIEW_QUEUE,
     enabled: !!id,
     select: (res) => res.data ?? null,
   })