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/app/admin/timer-actions.ts

@@ -0,0 +1,55 @@
+"use server";
+
+import { revalidatePath } from "next/cache";
+import { db } from "@/db";
+import { time_entries } from "@/db/schema";
+import { eq, isNull } from "drizzle-orm";
+import { nanoid } from "nanoid";
+
+export async function startTimer(clientId: string): Promise<{ entryId: string }> {
+  // Stop any currently running session (for any client) before starting a new one
+  const running = await db
+    .select({ id: time_entries.id })
+    .from(time_entries)
+    .where(isNull(time_entries.ended_at));
+
+  for (const r of running) {
+    const now = new Date();
+    const entry = await db
+      .select({ started_at: time_entries.started_at })
+      .from(time_entries)
+      .where(eq(time_entries.id, r.id))
+      .limit(1);
+    if (entry[0]) {
+      const secs = Math.round((now.getTime() - new Date(entry[0].started_at).getTime()) / 1000);
+      await db
+        .update(time_entries)
+        .set({ ended_at: now, duration_seconds: secs })
+        .where(eq(time_entries.id, r.id));
+    }
+  }
+
+  const id = nanoid();
+  await db.insert(time_entries).values({ id, client_id: clientId });
+  revalidatePath("/admin");
+  return { entryId: id };
+}
+
+export async function stopTimer(entryId: string): Promise<void> {
+  const rows = await db
+    .select({ started_at: time_entries.started_at })
+    .from(time_entries)
+    .where(eq(time_entries.id, entryId))
+    .limit(1);
+
+  if (!rows[0]) return;
+
+  const now = new Date();
+  const secs = Math.round((now.getTime() - new Date(rows[0].started_at).getTime()) / 1000);
+  await db
+    .update(time_entries)
+    .set({ ended_at: now, duration_seconds: secs })
+    .where(eq(time_entries.id, entryId));
+
+  revalidatePath("/admin");
+}