WP-00: project skeleton with three-level test harness

Cargo workspace (domain, application, infrastructure, api), axum health endpoint
with SPA fallback, Vue 3 + Tailwind frontend, Vitest, Playwright, Makefile,
Gitea Actions CI and README.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

.env.example

@@ -0,0 +1,12 @@
+# Backend configuration (copy to backend/.env for local development)
+DATABASE_URL=sqlite://data/monitoring.db?mode=rwc
+JWT_SECRET=change-me-to-a-long-random-string
+BIND=127.0.0.1:8080
+# Created on first start if no user exists
+BOOTSTRAP_ADMIN_EMAIL=admin@example.com
+BOOTSTRAP_ADMIN_PASSWORD=change-me-min-12-chars
+# Set to true behind HTTPS so the refresh cookie is marked Secure
+COOKIE_SECURE=false
+# Directory with the built frontend (served as SPA fallback)
+FRONTEND_DIR=../frontend/dist
+RUST_LOG=info,sqlx=warn