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/.env.vps.example

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+# Copy to ./.env on the VPS and fill in. Never commit the real .env.
+
+# Domain for Caddy automatic HTTPS. Point its DNS A record to this VPS IP first.
+DOMAIN=arbpulse.example.com
+
+NODE_ENV=production
+PORT=8080
+
+# Engine tuning (mirrors render.yaml production defaults)
+STALE_MS=3000
+FLICKER_CONFIRM_MS=150
+MIN_NET_PROFIT_PCT=0.0005
+MAX_TRADE_BTC=0.25
+LATENCY_MS=120
+LATENCY_SLIPPAGE_BPS=2
+CIRCUIT_BREAKER_LOSSES=5
+CIRCUIT_BREAKER_COOLDOWN_MS=15000
+INITIAL_USDT=50000
+INITIAL_BTC=0.5
+DEMO_MODE=false
+RECORD_FEED=false
+
+# Observability. Error monitoring is on when SENTRY_DSN is set.
+# Leave SENTRY_TRACING=false for 24/7 (keeps spans off the free-tier quota).
+SENTRY_DSN=
+SENTRY_TRACING=false
+LOG_LEVEL=info
+
+# Upstash (optional): rate limiting on /api/* + short-TTL snapshot cache.
+# Leave empty to disable both features.
+UPSTASH_REDIS_REST_URL=
+UPSTASH_REDIS_REST_TOKEN=