Add production observability: Sentry, pino, and sharp badge encoding.

Sentry is opt-in via DSN env vars; logger uses structured pino JSON in prod; badge uploads are normalized to GIF with sharp.

Co-authored-by: Cursor <[email protected]>

.env.example

@@ -76,5 +76,16 @@ PAYPAL_API=https://api-m.sandbox.paypal.com
 REDIS_URL=redis://127.0.0.1:6379
 
 # Logging level (debug | info | warn | error). Defaults to 'info' in production,
-# 'debug' in development.
+# 'debug' in development. Production logs use structured JSON via pino.
 LOG_LEVEL=info
+
+# Optional Sentry error monitoring (no-op when unset).
+# Server/edge use SENTRY_DSN; browser uses NEXT_PUBLIC_SENTRY_DSN.
+SENTRY_DSN=
+NEXT_PUBLIC_SENTRY_DSN=
+# Optional source-map upload during CI builds (requires SENTRY_AUTH_TOKEN).
+SENTRY_ORG=
+SENTRY_PROJECT=
+SENTRY_AUTH_TOKEN=
+# Optional release tag shown in Sentry (e.g. git sha).
+APP_VERSION=