SMB: optional legacy mode (SMB1 + NTLMv1) for old clients

Supermicro BMC virtual media ("CD-ROM image" over a Windows share) only
offers the SMB1 dialect "NT LM 0.12", which Samba rejects with
server min protocol = SMB2. Add an opt-in "Allow legacy clients" SMB
setting that renders server min protocol = NT1 and
ntlm auth = ntlmv1-permitted. Off by default.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/web/shares.go

@@ -204,6 +204,7 @@ func (s *Server) smbSettings(w http.ResponseWriter, r *http.Request) {
 	c.SMB.Enabled = r.FormValue("enabled") != ""
 	c.SMB.Workgroup = strings.ToUpper(strings.TrimSpace(r.FormValue("workgroup")))
 	c.SMB.ServerString = strings.TrimSpace(r.FormValue("server_string"))
+	c.SMB.Legacy = r.FormValue("legacy") != ""
 	if err := shares.ValidateComment(c.SMB.ServerString); err != nil {
 		s.sharesFail(w, r, "Not saved: server description: "+err.Error(), smbForm{}, nfsForm{})
 		return