Design overhaul, stats page, internal notes

Design: Onest+Unbounded font pairing (Cyrillic-verified, replacing plain
Golos Text), manual light/dark toggle wired to the data-theme cascade
already built in MVP-1, refreshed palette + new chart-mark tokens
(CVD-validated via the dataviz skill's validator), colored avatar
initials, per-channel colored badges, favicon, nicer empty states.

Stats: /stats page — status/channel breakdown, 14-day ticket volume,
avg first-response time, per-agent open-ticket workload. Colors and
chart forms follow the dataviz skill's procedure (categorical order
re-stepped to clear the CVD adjacency check in both themes).

Internal notes: messages.visibility ("public"/"internal") column.
Agent-only notes never reach customer-facing reads (getTicketForCustomer)
or the customer SSE stream (/api/portal/events, reused by the widget) —
fixed at both the initial-fetch and live-delivery layers.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QcXH24ky6zjk2UyK5oZUPH

src/app/(admin)/layout.tsx

@@ -3,6 +3,7 @@ import { Ticket } from "lucide-react";
 import { getCurrentSession } from "@/lib/auth/session";
 import { LogoutButton } from "./logout-button";
 import { NavLinks } from "./nav-links";
+import { ThemeToggle } from "./theme-toggle";
 
 export default async function AdminLayout({ children }: { children: React.ReactNode }) {
   const session = await getCurrentSession();
@@ -14,7 +15,7 @@ export default async function AdminLayout({ children }: { children: React.ReactN
     <div className="flex min-h-screen flex-col bg-bg">
       <header className="border-b border-border bg-surface">
         <div className="mx-auto flex max-w-7xl items-center gap-6 px-6 py-3">
-          <div className="flex items-center gap-2 font-bold tracking-tight">
+          <div className="flex items-center gap-2 font-display text-[15px] font-bold tracking-tight">
             <div className="flex h-7 w-7 items-center justify-center rounded-md bg-accent text-white">
               <Ticket size={15} strokeWidth={2.5} />
             </div>
@@ -23,6 +24,7 @@ export default async function AdminLayout({ children }: { children: React.ReactN
           <NavLinks />
           <div className="ml-auto flex items-center gap-3">
             <span className="text-sm text-text-muted">{session.user.name}</span>
+            <ThemeToggle />
             <LogoutButton />
           </div>
         </div>