tools: add mos-comms cross-agent git-relay package

Portable bash utility for two Mos orchestrators on separate hosts to relay
via a shared git branch: one-file-per-message (conflict-free), mechanical
systemd-timer poll, STATIC tmux wake-injection (no untrusted data in send-keys),
3x rebase-retry send, first-poll baseline (no history dump). See
tools/mos-comms/MOS-COMMS-PROTOCOL.md for the spec, threat model, and install.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tools/mos-comms/systemd/mos-comms.service

@@ -0,0 +1,6 @@
+[Unit]
+Description=Mos cross-host git communications poll
+
+[Service]
+Type=oneshot
+ExecStart=%h/.local/bin/mos-comms.sh poll

tools/mos-comms/systemd/mos-comms.timer

@@ -0,0 +1,9 @@
+[Unit]
+Description=Poll Mos cross-host git communications
+
+[Timer]
+OnBootSec=2min
+OnUnitActiveSec=15min
+
+[Install]
+WantedBy=timers.target