Shares of other services and RepoISO integration

- include SMB drop-ins from /etc/samba/smb.conf.d into the generated smb.conf
- keep smbd/nfs-server running while other services (/etc/exports.d, drop-ins) share,
  instead of disabling them when nasmon has no shares of its own
- list those shares read-only on /shares
- settings: RepoISO URL; poll its /api/integration/status, dashboard card, menu link,
  alerts for portal down, stale worker, failed jobs, unmounted publications

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

internal/web/handlers.go

@@ -465,6 +465,7 @@ func formToSettings(r *http.Request, old config.Settings) config.Settings {
 	c.SelfTests.ShortDays = num("st_short_days", old.SelfTests.ShortDays)
 	c.SelfTests.LongDays = num("st_long_days", old.SelfTests.LongDays)
 	c.SelfTests.Hour = num("st_hour", old.SelfTests.Hour)
+	c.Integrations.RepoISOURL = strings.TrimSpace(r.FormValue("repoiso_url"))
 	return c
 }