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/lib/constants.ts

@@ -30,6 +30,8 @@ export const PROB_MEDIUM = 0.5
 export const STALE_PROPERTIES = 5 * 60 * 1000
 export const STALE_MATCHES = 2 * 60 * 1000
 export const STALE_SIGNALS = 5 * 60 * 1000
+export const STALE_MARKET_SIGNALS = 30 * 1000  // aggressive — market leads refresh often
+export const STALE_REVIEW_QUEUE = 30 * 1000    // aggressive — ops team works in real-time
 
 // Route paths — single source of truth
 export const ROUTES = {