feat: lead → client conversion + client contact fields (email/phone)

Blocco A+B (milestone v2.3). Migration 0011 is additive (ADD COLUMN only):
clients.email, clients.phone, leads.archived.

- createClientCore() extracted from createClient and reused by conversion
- clients.email/phone added to create + edit forms and shown on client header
  (never exposed on the public /client/[token] page)
- convertLeadToClient(): reuses core, carries over lead transcripts
  (client_transcripts.client_id), links project.created_from_lead_id,
  archives the lead while keeping its "won" status; idempotent
- "Converti in cliente" button on won leads; "Convertito → Apri cliente"
  once converted (clientId resolved via created_from_lead_id)
- archived leads hidden from list/kanban; detail page fetches by id incl. archived

Migration must be applied to the prod DB BEFORE this is deployed.

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

src/app/admin/clients/[id]/actions.ts

@@ -50,10 +50,17 @@ async function resolveEntity(id: string): Promise<{ projectId: string | null; pa
 
 // ── CLIENT CRUD ───────────────────────────────────────────────────────────────
 
+const emptyToNull = (v: unknown) => {
+  const s = typeof v === "string" ? v.trim() : "";
+  return s === "" ? null : s;
+};
+
 const clientSchema = z.object({
   name:       z.string().min(1, "Nome richiesto"),
   brand_name: z.string().min(1, "Brand name richiesto"),
   brief:      z.string(),
+  email:      z.string().optional().transform(emptyToNull),
+  phone:      z.string().optional().transform(emptyToNull),
   slug: z
     .string()
     .regex(/^[a-z0-9-]{3,50}$/, "Slug non valido (es. mario-rossi, min 3 max 50 caratteri)")
@@ -68,6 +75,8 @@ export async function updateClient(clientId: string, formData: FormData) {
     name:       formData.get("name"),
     brand_name: formData.get("brand_name"),
     brief:      formData.get("brief") ?? "",
+    email:      formData.get("email") ?? "",
+    phone:      formData.get("phone") ?? "",
     slug:       formData.get("slug") ?? "",
   });
   if (!parsed.success) throw new Error(parsed.error.issues[0].message);