feat(cloak): wire cloak into the deploy path for windows* deckies

Base containers whose nmap_os has a mangle profile now build the cloak image
(FROM the per-decky distro), ship the light decnet subtree, and run
'python -m decnet.cloak' alongside holding the MACVLAN IP — netns-safe (cloak
backgrounded behind 'exec sleep infinity' so a cloak crash never tears down the
base/netns). composer injects build/command/NET_RAW/env (DECNET_NMAP_OS,
DECNET_OPEN_PORTS, DECKY_IP); deployer._sync_cloak_sources syncs the subtree;
non-windows deckies are unchanged. Mangler signal-guarded for thread use;
entry runs mangler in main thread, responder as daemon.

Verified live: real path makes nmap -O read 'Microsoft Windows Server 2012/2016'
with handshakes intact.

.gitignore

@@ -85,3 +85,6 @@ testfail
 # Internal design/dev notes — not for publication
 /development/
 decnet.tar
+
+# cloak base-image build context: decnet subtree synced in at deploy time
+decnet/templates/_shared/cloak/decnet/