feat: client edit/delete/archive + time tracker + analytics time section

Schema:
- clients.archived boolean (default false)
- time_entries table (client_id, started_at, ended_at, duration_seconds)

Client management:
- /admin/clients/[id]/edit — form pre-compilato con nome, brand, brief
- ClientActions: Modifica / Archivia / Elimina con doppia conferma
- setClientArchived: toggle archiviazione senza perdere dati
- deleteClient: elimina con cascade, redirect a /admin
- Admin list: toggle "Mostra archiviati" via ?archived=1, righe archiviate opache

Time tracker:
- startTimer: crea sessione, ferma automaticamente quella precedente
- stopTimer: chiude sessione, calcola duration_seconds
- TimerCell: ▶/⏹ per ogni cliente, contatore live in secondi, totale cumulativo
- Una sola sessione attiva alla volta su tutta la lista

Analytics:
- Sezione "Fatturato" (invariata) + sezione "Tempo tracciato" separata
- Ore totali per anno + barre orizzontali per cliente
- getTotalTrackedHours, getTimeByClient queries

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

src/components/admin/TimerCell.tsx

@@ -0,0 +1,91 @@
+"use client";
+
+import { useState, useEffect, useTransition } from "react";
+import { useRouter } from "next/navigation";
+import { startTimer, stopTimer } from "@/app/admin/timer-actions";
+
+function formatDuration(seconds: number): string {
+  const h = Math.floor(seconds / 3600);
+  const m = Math.floor((seconds % 3600) / 60);
+  const s = seconds % 60;
+  if (h > 0) return `${h}:${String(m).padStart(2, "0")}:${String(s).padStart(2, "0")}`;
+  return `${m}:${String(s).padStart(2, "0")}`;
+}
+
+export function TimerCell({
+  clientId,
+  activeEntryId,
+  activeStartedAt,
+  totalTrackedSeconds,
+}: {
+  clientId: string;
+  activeEntryId: string | null;
+  activeStartedAt: Date | null;
+  totalTrackedSeconds: number;
+}) {
+  const router = useRouter();
+  const [, startTransition] = useTransition();
+  const isRunning = activeEntryId !== null;
+
+  // Live elapsed counter
+  const [elapsed, setElapsed] = useState(() => {
+    if (!activeStartedAt) return 0;
+    return Math.round((Date.now() - new Date(activeStartedAt).getTime()) / 1000);
+  });
+
+  useEffect(() => {
+    if (!isRunning) { setElapsed(0); return; }
+    const start = activeStartedAt ? new Date(activeStartedAt).getTime() : Date.now();
+    const tick = () => setElapsed(Math.round((Date.now() - start) / 1000));
+    tick();
+    const id = setInterval(tick, 1000);
+    return () => clearInterval(id);
+  }, [isRunning, activeStartedAt]);
+
+  function handleToggle() {
+    startTransition(async () => {
+      if (isRunning && activeEntryId) {
+        await stopTimer(activeEntryId);
+      } else {
+        await startTimer(clientId);
+      }
+      router.refresh();
+    });
+  }
+
+  const displayTotal = formatDuration(totalTrackedSeconds + (isRunning ? elapsed : 0));
+
+  return (
+    <div className="flex items-center gap-2">
+      <button
+        onClick={handleToggle}
+        title={isRunning ? "Ferma timer" : "Avvia timer"}
+        className={`w-7 h-7 rounded-full flex items-center justify-center transition-colors shrink-0 ${
+          isRunning
+            ? "bg-red-100 text-red-600 hover:bg-red-200"
+            : "bg-[#1A463C]/10 text-[#1A463C] hover:bg-[#1A463C]/20"
+        }`}
+      >
+        {isRunning ? (
+          // Stop square
+          <svg className="w-3 h-3" fill="currentColor" viewBox="0 0 16 16">
+            <rect x="3" y="3" width="10" height="10" rx="1.5" />
+          </svg>
+        ) : (
+          // Play triangle
+          <svg className="w-3 h-3" fill="currentColor" viewBox="0 0 16 16">
+            <path d="M4 3.5v9l9-4.5-9-4.5z" />
+          </svg>
+        )}
+      </button>
+
+      <span
+        className={`text-xs tabular-nums font-mono ${
+          isRunning ? "text-red-600 font-semibold" : "text-[#71717a]"
+        }`}
+      >
+        {isRunning ? formatDuration(elapsed) : displayTotal}
+      </span>
+    </div>
+  );
+}