Apply demo-activity-bot: Bruno, the synthetic public-walk generator

Adds a background demo user (`bruno`) plus two pg-boss jobs that generate
public trekking routes and activities in inner Berlin and prune them
after 14 days. Disabled by default everywhere; flip `DEMO_BOT_ENABLED`
only in prod.

- Schema: `synthetic` boolean on routes + activities
- `ensureDemoUser()` idempotent insert + badge on /users/bruno
- Generation gate: 07-21 Berlin local, p=0.12, 40-route cap in 14d
- Initial 4-walk backfill on first enable; retention via daily prune
- Prometheus gauges `demo_bot_synthetic_routes_total` / `_activities_total`
- Unit + DB-gated integration + E2E tests

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

infrastructure/.env.example

@@ -6,3 +6,11 @@ POSTGRES_PASSWORD=change-me
 JWT_SECRET=change-me
 S3_ACCESS_KEY=
 S3_SECRET_KEY=
+
+# Demo-activity-bot (Bruno). Only enable in prod. When true, the journal
+# worker bootstraps a `bruno` user and generates public demo routes +
+# activities every 90 min. Set DEMO_BOT_REGION to override the default
+# Berlin bbox — JSON {"bbox":[w,s,e,n]}. Retention is in days (default 14).
+# DEMO_BOT_ENABLED=true
+# DEMO_BOT_RETENTION_DAYS=14
+# DEMO_BOT_REGION={"bbox":[13.25,52.45,13.55,52.60]}