feat(comms): P1 presence — minimal Synapse + fleet presence room + mosaic.presence heartbeat + liveness (#888)

Co-authored-by: jason.woltje <jason@diversecanvas.com>
Co-committed-by: jason.woltje <jason@diversecanvas.com>

infra/matrix/dev-down.sh

@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+# dev-down.sh — tear down the DEV Synapse (matrix-p1-dev). DEV-ONLY.
+#   ./dev-down.sh            # stop + remove containers, keep ./.data
+#   ./dev-down.sh --purge    # also delete ./.data (fresh next bring-up)
+set -euo pipefail
+HERE="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+docker compose -f "${HERE}/docker-compose.dev.yml" --profile element down -v --remove-orphans || true
+if [[ "${1:-}" == "--purge" ]]; then
+  rm -rf "${HERE}/.data"
+  echo "[dev-down] purged ${HERE}/.data"
+fi
+echo "[dev-down] matrix-p1-dev stopped"