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>

.env.example

@@ -0,0 +1,39 @@
+# =============================================================================
+# Matrix stack configuration
+# Copy this file to ".env" and fill in real values before starting the stack.
+# ".env" is git-ignored on purpose: it is the only place where your real
+# domain name and secrets live.
+# =============================================================================
+
+# --- Domain ------------------------------------------------------------------
+# Bare domain used as the Matrix server_name (this is what ends up in every
+# user id: @user:DOMAIN). A DNS A/AAAA record for DOMAIN and for each
+# subdomain below must point to this server's IP.
+DOMAIN=example.com
+
+# Subdomains (each needs its own DNS record pointing here)
+MATRIX_SUBDOMAIN=matrix
+ELEMENT_SUBDOMAIN=element
+ADMIN_SUBDOMAIN=admin
+TRAEFIK_SUBDOMAIN=traefik
+
+# --- Traefik / Let's Encrypt ---------------------------------------------------
+# Email used for Let's Encrypt account registration and expiry notices.
+ACME_EMAIL=changeme@example.com
+
+# htpasswd credentials for the Traefik dashboard (traefik.DOMAIN).
+# Generate your own with:
+#   openssl passwd -apr1
+# Format: user:hash  (escape any literal "$" as "$$" if you edit this by hand
+# outside of a real .env file consumed by docker compose)
+TRAEFIK_DASHBOARD_AUTH='admin:changeme'
+
+# --- PostgreSQL (Synapse database) -------------------------------------------
+POSTGRES_DB=synapse
+POSTGRES_USER=synapse
+POSTGRES_PASSWORD=changeme
+
+# --- Synapse -------------------------------------------------------------------
+# Shared secret used only once, to create the first admin account via
+# `register_new_matrix_user`. Generate with: openssl rand -hex 32
+REGISTRATION_SHARED_SECRET=changeme