feat: global time range context with custom date picker

Lift time range state into a shared React context so the selected
range persists across page navigation and browser refreshes
(localStorage). Add a "Custom" option with a popover date picker
that lets users specify arbitrary start/end dates. All preset end
times now use endOf("day") (23:59:59) instead of the current moment.

components/ClientProviders.tsx

@@ -4,6 +4,7 @@ import { type ReactNode } from "react";
 import { usePathname } from "next/navigation";
 import { I18nProvider } from "@/lib/i18n";
 import { ThemeProvider } from "@/lib/theme";
+import { TimeRangeProvider } from "@/lib/time-range-context";
 import { Sidebar } from "@/components/Sidebar";
 
 export function ClientProviders({ children }: { children: ReactNode }) {
@@ -13,14 +14,16 @@ export function ClientProviders({ children }: { children: ReactNode }) {
   return (
     <ThemeProvider>
       <I18nProvider>
-        {isPortal ? (
-          <>{children}</>
-        ) : (
-          <>
-            <Sidebar />
-            <main className="ml-[220px] min-h-screen p-6 lg:p-8">{children}</main>
-          </>
-        )}
+        <TimeRangeProvider>
+          {isPortal ? (
+            <>{children}</>
+          ) : (
+            <>
+              <Sidebar />
+              <main className="ml-[220px] min-h-screen p-6 lg:p-8">{children}</main>
+            </>
+          )}
+        </TimeRangeProvider>
       </I18nProvider>
     </ThemeProvider>
   );