fix(renderer): use snapshot.currentCompanyId as single source of truth (D-03)

CompanySlice's standalone currentCompanyId field + setCurrentCompanyId action
were never written by any caller, so useDesktopEvents.ts read null and fell
through to full refresh for every entity event -- the granular patch
machinery was dead code.

- Remove currentCompanyId field + setCurrentCompanyId from CompanySlice
- refreshBadges reads from snapshot.currentCompanyId
- useDesktopEvents reads companyId from snapshot.currentCompanyId
- Update store unit test to seed snapshot instead of calling removed action

src/renderer/hooks/useDesktopEvents.ts

@@ -13,7 +13,7 @@ export function useDesktopEvents(
     const store = useAppStore;
 
     async function handleGranularBatch(events: GranularEventEntry[]) {
-      const companyId = store.getState().currentCompanyId;
+      const companyId = store.getState().snapshot?.currentCompanyId ?? null;
       if (!companyId) {
         void refreshRef.current();
         return;