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/templates/shares.html

@@ -18,6 +18,7 @@
     <label class="check"><input type="checkbox" name="enabled" value="1" {{if .C.SMB.Enabled}}checked{{end}}> SMB server enabled</label>
     <label>Workgroup <input name="workgroup" value="{{.C.SMB.Workgroup}}"></label>
     <label>Description <input name="server_string" value="{{.C.SMB.ServerString}}"></label>
+    <label class="check"><input type="checkbox" name="legacy" value="1" {{if .C.SMB.Legacy}}checked{{end}}> Allow legacy clients (SMB1 + NTLMv1) — IPMI/BMC virtual media, old devices; less secure</label>
     <div class="field"><span class="field-name">&nbsp;</span><span><button type="submit" class="secondary">Save SMB settings</button></span></div>
   </form>