Fix overview error rate panel, add request metrics to journal

Dashboard: switch error rate panel from app-level http_request_duration
(never observed) to Caddy's caddy_http_response_duration_seconds_count.

Journal: add custom server.ts (matching planner pattern) that observes
http_request_duration_seconds on every request. Replaces react-router-serve
with a custom Node HTTP server that handles /api/health, /api/metrics,
static assets, and request timing. Removes redundant React Router routes
for health and metrics.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

infrastructure/docker-compose.yml

@@ -35,7 +35,7 @@ services:
       WAHOO_CLIENT_SECRET: ${WAHOO_CLIENT_SECRET:-}
       WAHOO_WEBHOOK_TOKEN: ${WAHOO_WEBHOOK_TOKEN:-}
     healthcheck:
-      test: ["CMD-SHELL", "curl -sf http://localhost:3000/api/health || exit 1"]
+      test: ["CMD-SHELL", "node -e \"fetch('http://localhost:3000/api/health').then(r=>{process.exit(r.ok?0:1)}).catch(()=>process.exit(1))\""]
       interval: 15s
       timeout: 5s
       retries: 3