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]/edit/page.tsx

@@ -62,6 +62,29 @@ export default async function EditClientPage({
           />
         </div>
 
+        <div className="grid grid-cols-1 sm:grid-cols-2 gap-4">
+          <div className="space-y-1.5">
+            <Label htmlFor="email">Email</Label>
+            <Input
+              id="email"
+              name="email"
+              type="email"
+              defaultValue={client.email ?? ""}
+              placeholder="marco@rossistudio.it"
+            />
+          </div>
+          <div className="space-y-1.5">
+            <Label htmlFor="phone">Telefono</Label>
+            <Input
+              id="phone"
+              name="phone"
+              type="tel"
+              defaultValue={client.phone ?? ""}
+              placeholder="+39 333 1234567"
+            />
+          </div>
+        </div>
+
         <div className="space-y-1.5">
           <Label htmlFor="brief">Brief progetto</Label>
           <Textarea