fix(admin): SQL GROUP BY in reports, hydration in settings, mobile tabs scroll

- reports.ts: wrap window-function arg in SUM() so it operates on the
  per-group aggregate instead of the raw c.id column (PostgreSQL
  rejects window funcs over non-grouped, non-aggregated columns).
- SettingsClient.tsx: read URL hash in useEffect instead of a lazy
  useState initializer to avoid server/client first-render mismatch
  on tab content (was triggering full client re-render in /admin/settings).
- layout.tsx: add pt-16 lg:pt-0 to page-content for mobile header clearance.
- ReportsDashboard.tsx: memoize DateRange on primitive inputs to break
  useEffect → setState → re-render loop caused by buildRange returning
  a new object every call.
- AdminFilterTabs.tsx: add overflow-x-auto so wide tab rows scroll on
  mobile instead of overflowing.
- use-media-query.ts: always start as false for hydration safety; callers
  handle the mobile/unknown branch first.

src/components/admin/SettingsClient.tsx

@@ -135,14 +135,17 @@ export default function SettingsClient({
   paymentSettings,
   currentUser,
 }: Props) {
-  // Initial tab is determined by URL hash if present, otherwise "general".
-  // No useEffect needed — we read window.location.hash during the lazy
-  // initializer on the client. On the server we default to "general".
-  const [activeTab, setActiveTab] = useState<Tab>(() => {
-    if (typeof window === "undefined") return "general";
+  // Server renders the default tab; client picks up the URL hash after mount
+  // so the initial server HTML matches the first client render (avoids
+  // hydration mismatch). Reading window.location.hash in a lazy initializer
+  // is unsafe because the server has no hash and would render a different
+  // tab than the client.
+  const [activeTab, setActiveTab] = useState<Tab>("general");
+  useEffect(() => {
     const hash = window.location.hash.slice(1);
-    return TABS.find((t) => t.hash === hash)?.id ?? "general";
-  });
+    const tab = TABS.find((t) => t.hash === hash)?.id;
+    if (tab) setActiveTab(tab);
+  }, []);
 
   return (
     <main className="min-h-screen bg-[var(--admin-bg)]">