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/shares/shares_test.go

@@ -225,6 +225,7 @@ func newManager(f *fake) *Manager {
 	m := New(f.run)
 	m.LookPath = f.lookPath
 	m.Owner, m.UID, m.GID = "ansible", "1000", "1000"
+	m.IncludeDir, m.ExportsDir = "", "" // never read the host's drop-ins in tests
 	return m
 }