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>

playwright.config.ts

@@ -47,6 +47,14 @@ export default defineConfig({
         baseURL: "http://localhost:3000",
       },
     },
+    {
+      name: "demo-bot",
+      testMatch: "demo-bot.test.ts",
+      use: {
+        ...devices["Desktop Chrome"],
+        baseURL: "http://localhost:3000",
+      },
+    },
     {
       name: "integration",
       testMatch: "integration.test.ts",