chore(deploy): add VPS deploy artifacts (Docker Compose + Caddy + runbook)

Self-contained VPS deployment for 24/7 operation: app container behind Caddy with automatic HTTPS, idempotent deploy.sh, .env template, and runbook. SENTRY_TRACING defaults off to stay within the Sentry free-tier span quota.

Co-authored-by: Cursor <cursoragent@cursor.com>

deploy/Caddyfile

@@ -0,0 +1,9 @@
+# Automatic HTTPS via Let's Encrypt. DOMAIN comes from ./.env (docker compose
+# substitutes ${DOMAIN}). Point the domain's DNS A record to this VPS first.
+{$DOMAIN} {
+	# flush_interval -1 disables response buffering so SSE (/api/stream) streams
+	# in real time. Do NOT gzip event-stream responses (would buffer them).
+	reverse_proxy app:8080 {
+		flush_interval -1
+	}
+}