feat: pagina Conversazioni — inbox unificata messaggi clienti

Nuova pagina admin /admin/conversazioni: vista WhatsApp-style (lista
conversazioni a sinistra, thread + risposta a destra) che aggrega i
messaggi di tutti i clienti dalla tabella comments, cross-cliente.

- Migration additiva 0014: clients.admin_last_read_at per tracciare
  letto/non-letto (pallini + badge in sidebar). Applicata a prod.
- conversations-queries.ts: aggregazione entity_id → cliente
  (general/phase/task/deliverable), getConversations /
  getConversationThread / getUnreadConversationsCount.
- Risposte admin salvate come commento "general" (visibili anche nella
  chat cliente e nel CommentsTab della scheda).
- Voce di menu + badge non-letti (AdminSidebar/AdminShell/layout).
- Token semantici per dual light/dark; refresh manuale (no polling).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/admin/conversazioni/actions.ts

@@ -0,0 +1,59 @@
+"use server";
+
+import { revalidatePath } from "next/cache";
+import { getServerSession } from "next-auth";
+import { eq } from "drizzle-orm";
+import { authOptions } from "@/lib/auth";
+import { db } from "@/db";
+import { clients, comments } from "@/db/schema";
+
+async function requireAdmin() {
+  const session = await getServerSession(authOptions);
+  if (!session) throw new Error("Non autorizzato");
+}
+
+/**
+ * Admin reply from the Conversazioni inbox. Per project decision, replies are
+ * saved as a "general" comment on the client (entity_id = clientId), so they
+ * surface in the client's general chat and in the client detail CommentsTab.
+ */
+export async function replyToConversation(clientId: string, formData: FormData) {
+  await requireAdmin();
+  const body = (formData.get("body") as string)?.trim();
+  if (!clientId || !body) throw new Error("Dati mancanti");
+
+  // Validate the client exists (entity_id integrity).
+  const rows = await db
+    .select({ id: clients.id })
+    .from(clients)
+    .where(eq(clients.id, clientId))
+    .limit(1);
+  if (rows.length === 0) throw new Error("Cliente non trovato");
+
+  await db.insert(comments).values({
+    entity_type: "general",
+    entity_id: clientId,
+    author: "admin",
+    body,
+  });
+
+  // Replying implies the admin has read the incoming messages.
+  await db
+    .update(clients)
+    .set({ admin_last_read_at: new Date() })
+    .where(eq(clients.id, clientId));
+
+  revalidatePath("/admin/conversazioni");
+  revalidatePath(`/admin/clients/${clientId}`);
+}
+
+/** Mark a client's conversation as read up to now (clears unread dot/badge). */
+export async function markConversationRead(clientId: string) {
+  await requireAdmin();
+  if (!clientId) return;
+  await db
+    .update(clients)
+    .set({ admin_last_read_at: new Date() })
+    .where(eq(clients.id, clientId));
+  revalidatePath("/admin/conversazioni");
+}