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>

apps/journal/app/lib/metrics.server.ts

@@ -10,4 +10,19 @@ export const httpRequestDuration = new client.Histogram({
   buckets: [0.01, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5],
 });
 
+/**
+ * Count of synthetic demo-bot routes currently in the database. Scraped
+ * by the background worker after each generation run so the Grafana
+ * board stays live without a /metrics handler on the worker process.
+ */
+export const demoBotSyntheticRoutesTotal = new client.Gauge({
+  name: "demo_bot_synthetic_routes_total",
+  help: "Total synthetic demo-bot routes currently stored",
+});
+
+export const demoBotSyntheticActivitiesTotal = new client.Gauge({
+  name: "demo_bot_synthetic_activities_total",
+  help: "Total synthetic demo-bot activities currently stored",
+});
+
 export const registry = client.register;