Initial commit: Matrix stack (Synapse + Synapse-Admin + Element Web) behind Traefik

Fully dockerized deployment with automatic Let's Encrypt certificates via
Traefik's static file provider (no docker.sock needed), bind-mounted data
folders instead of named volumes, and domain/secrets kept out of git via
.env + rendered templates.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

scripts/render-templates.sh

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+# Renders *.template files into their real config counterparts using the
+# values from .env. Run this after every edit of .env, before
+# `docker compose up`.
+set -euo pipefail
+cd "$(dirname "$0")/.."
+
+if [ ! -f .env ]; then
+    echo "Missing .env — copy .env.example to .env and edit it first." >&2
+    exit 1
+fi
+
+set -a
+# shellcheck disable=SC1091
+source .env
+set +a
+
+VARS='${DOMAIN} ${MATRIX_SUBDOMAIN} ${ELEMENT_SUBDOMAIN} ${ADMIN_SUBDOMAIN} ${TRAEFIK_SUBDOMAIN}'
+
+envsubst "$VARS" < element/config/config.json.template > element/config/config.json
+envsubst "$VARS" < synapse-admin/config/config.json.template > synapse-admin/config/config.json
+envsubst "$VARS" < wellknown/well-known-matrix-client.json.template > wellknown/html/well-known-matrix-client.json
+envsubst "$VARS" < traefik/dynamic/routes.yml.template > traefik/dynamic/routes.yml
+
+echo "Rendered config for domain: ${DOMAIN}"