feat: add custom date range picker, fix country click highlight on map

- Analytics default interval changed to 1h
- Add 'Custom' toggle option with datetime-local pickers (pre-filled to last 24h)
- Refactor analytics-db: buildWhere now takes from/to unix timestamps instead of Interval
- Export INTERVAL_SECONDS from analytics-db for route reuse
- All 6 API routes accept from/to params (fallback to interval if absent)
- Timeline bucket size computed from duration rather than hardcoded per interval
- Fix map country click highlight: bake isSelected into GeoJSON features (data-driven)
  instead of relying on Layer filter prop updates (unreliable in react-map-gl v8)
- Split highlight into countries-selected (data-driven) and countries-hover (filter-driven)
- Show tooltip at country centroid when selected via table, hover takes precedence

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/api/analytics/user-agents/route.ts

@@ -1,12 +1,24 @@
 import { NextRequest, NextResponse } from 'next/server';
 import { requireUser } from '@/src/lib/auth';
-import { getAnalyticsUserAgents, type Interval } from '@/src/lib/analytics-db';
+import { getAnalyticsUserAgents, INTERVAL_SECONDS } from '@/src/lib/analytics-db';
 
 export async function GET(req: NextRequest) {
   await requireUser();
   const { searchParams } = req.nextUrl;
-  const interval = (searchParams.get('interval') ?? '24h') as Interval;
   const host = searchParams.get('host') ?? 'all';
-  const data = await getAnalyticsUserAgents(interval, host);
+  const { from, to } = resolveRange(searchParams);
+  const data = await getAnalyticsUserAgents(from, to, host);
   return NextResponse.json(data);
 }
+
+function resolveRange(params: URLSearchParams): { from: number; to: number } {
+  const fromParam = params.get('from');
+  const toParam = params.get('to');
+  if (fromParam && toParam) {
+    return { from: parseInt(fromParam, 10), to: parseInt(toParam, 10) };
+  }
+  const interval = params.get('interval') ?? '1h';
+  const to = Math.floor(Date.now() / 1000);
+  const from = to - (INTERVAL_SECONDS[interval as keyof typeof INTERVAL_SECONDS] ?? INTERVAL_SECONDS['1h']);
+  return { from, to };
+}