perf: consolidate 7 dashboard hooks into single batch request

Replace useDashboardOverview, useDashboardPages, useDashboardLocations,
useDashboardDevices, useDashboardReferrers, useDashboardPerformance, and
useDashboardGoals with a single useDashboard hook that calls the existing
/dashboard batch endpoint. This endpoint runs all queries in parallel on
the backend and caches the result in Redis (30s TTL).

Reduces dashboard requests from 12 to 6 per refresh cycle (50% reduction).
At 1,000 concurrent users: ~6,000 req/min instead of 12,000.

CHANGELOG.md

@@ -6,6 +6,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 
 ## [Unreleased]
 
+### Improved
+
+- **Even faster dashboard loading.** Your dashboard now fetches all its data — pages, locations, devices, referrers, performance, and goals — in a single request instead of seven separate ones. This means the entire dashboard appears at once rather than sections loading one by one, and puts much less strain on the server when many people are viewing their analytics at the same time.
+
 ### Added
 
 - **Interactive 3D Globe.** The Locations panel now has a "Globe" tab showing your visitor locations on a beautiful, interactive 3D globe. Drag to rotate, and orange markers highlight where your visitors are — sized by how much traffic each country sends. The globe slowly auto-rotates and adapts to light and dark mode.