A shop can be renamed and, while empty, removed - from head office

The display name was always meant to be editable and the slug frozen;
until now neither had a way in. PATCH /api/sites/{site} takes a name
and a timezone (manager and above), DELETE removes an empty shop
(owner). The shop drawer in head office gets both, with the short name
shown read-only and the reason beside it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KGcjxF1cNLcuwc3DAPcnfj

server/internal/store/api_admin_clients.go

@@ -146,3 +146,15 @@ func (s *Store) DeleteEmptySite(ctx context.Context, clientID, siteID string) (s
 	}
 	return username, tx.Commit(ctx)
 }
+
+func (s *Store) UpdateSite(ctx context.Context, clientID, siteID string, in api.SiteUpdate) (api.SiteHealth, error) {
+	var out api.SiteHealth
+	err := s.pool.QueryRow(ctx, `
+		UPDATE sites
+		   SET name     = COALESCE($3, name),
+		       timezone = COALESCE($4, timezone)
+		 WHERE id = $1::uuid AND client_id = $2::uuid
+		RETURNING id::text, slug, name, timezone`, siteID, clientID, in.Name, in.Timezone).
+		Scan(&out.SiteID, &out.Slug, &out.Name, &out.Timezone)
+	return out, err
+}