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/mos-comms.config.example

@@ -0,0 +1,23 @@
+# Copy to ~/.config/mos-comms/mos-comms.config (mode 600) or point
+# MOS_COMMS_CONFIG at another local-only file. Do not commit this file with
+# operator values or credentials.
+
+# Required deployment identity; letters, numbers, dots, and hyphens only.
+AGENT_NAME="host-a-mos"
+
+# Required: URL/path of the shared, operator-provisioned git repository.
+# Authentication is delegated to git or the optional credential helper below.
+COMMS_REMOTE=""
+
+# Optional local paths and branch.
+COMMS_REPO_DIR="$HOME/.local/state/mos-comms/repo"
+COMMS_BRANCH="mos-comms"
+STATE_DIR="$HOME/.local/state/mos-comms"
+
+# Empty selects tmux's default socket. Set only when a named socket is used.
+TMUX_SOCKET=""
+TMUX_SESSION="mos-claude"
+
+# Optional git credential-helper name/path. Never place credential values here.
+# Example: GIT_CRED_HELPER="cache"
+GIT_CRED_HELPER=""